diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8f58d67..5fac148 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+## 1.0.1
+
+- `write` 新增可选 `serialPortIndex` 参数；传入时直接写入指定端口且不修改当前活跃端口，省略时保持原有活跃端口行为。
+
 ## 1.0.0
 
 - 重构插件代码,完整对接 CH934X Android SDK 文档中定义的全部接口:
diff --git a/android/src/main/java/com/xiarui/ch934x_serial/Ch934xSerialPlugin.java b/android/src/main/java/com/xiarui/ch934x_serial/Ch934xSerialPlugin.java
index 439024f..3728831 100644
--- a/android/src/main/java/com/xiarui/ch934x_serial/Ch934xSerialPlugin.java
+++ b/android/src/main/java/com/xiarui/ch934x_serial/Ch934xSerialPlugin.java
@@ -584,9 +584,14 @@ public class Ch934xSerialPlugin implements FlutterPlugin, MethodCallHandler, Act
         if (data == null || data.length == 0) {
             return 0;
         }
+        Integer portIndex = call.argument("serialPortIndex");
+        int idx = portIndex != null ? portIndex : activeSerialNumber;
+        if (idx < 0) {
+            return 0;
+        }
         try {
             return CH934XManager.getInstance().writeData(
-                    activeDevice, activeSerialNumber, data, data.length, 2000);
+                    activeDevice, idx, data, data.length, 2000);
         } catch (ChipException e) {
             return 0;
         }
diff --git a/docs/CH934X_Plugin_使用说明.md b/docs/CH934X_Plugin_使用说明.md
index f360c29..35d8618 100644
--- a/docs/CH934X_Plugin_使用说明.md
+++ b/docs/CH934X_Plugin_使用说明.md
@@ -161,11 +161,14 @@ await plugin.closePort();
 ### 3.3 串口读写
 
 ```dart
-// 写入
+// 写入当前活跃端口（向后兼容）
 final bytes = Uint8List.fromList([0x01, 0x02, 0x03]);
 final written = await plugin.write(bytes);
 debugPrint('写入字节数: $written');
 
+// 写入指定端口，不改变当前活跃端口；多端口客户端应使用此形式。
+final portWritten = await plugin.write(bytes, serialPortIndex: 2);
+
 // 读取(单次)
 final recv = await plugin.read(1024);
 if (recv.isEmpty) debugPrint('暂无数据');
@@ -182,13 +185,13 @@ await sub.cancel();
   - `length <= 0` 时**不会调用原生层**,直接返回空数组。
   - SDK 的 `readData` 会返回内部缓冲的所有数据,插件按
     `min(data.length, length)` 截断后回传。
-- `write(data)` 返回实际写入字节数,失败时为 0。
+- `write(data, serialPortIndex: n)` 返回实际写入字节数；传入端口时直接写入该端口且不改变当前活跃端口，失败时为 0。省略 `serialPortIndex` 时保持原有的当前活跃端口行为。
 - `dataStream` 默认 `chunkSize = 1024`、`interval = 20ms`,内部
   持续以 [interval] 为周期反复调用 `read`;当底层无数据时返回
   空缓冲区,消费者可据此判定。`chunkSize <= 0` 会抛
   `ArgumentError`。
 - 业务方在 widget dispose 时记得 `cancel` 订阅并 `closePort`。
-- `read`/`write` 都针对**当前活跃串口**;切换串口用 `setActivePort`。
+- `read` 默认针对当前活跃串口，也可传入显式端口；`write` 省略 `serialPortIndex` 时针对当前活跃串口，传入时直接写入指定端口。多端口并发客户端应使用显式端口写入，避免通过 `setActivePort` 共享切换端口。
 
 ### 3.4 GPIO 接口
 
diff --git a/example/pubspec.lock b/example/pubspec.lock
index 190501a..f4a6c1a 100644
--- a/example/pubspec.lock
+++ b/example/pubspec.lock
@@ -6,7 +6,7 @@ packages:
     description:
       name: async
       sha256: e2eb0491ba5ddb6177742d2da23904574082139b07c1e33b8503b9f46f3e1a37
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.13.1"
   boolean_selector:
@@ -14,7 +14,7 @@ packages:
     description:
       name: boolean_selector
       sha256: "8aab1771e1243a5063b8b0ff68042d67334e3feab9e95b9490f9a6ebf73b42ea"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.2"
   ch934x_serial:
@@ -23,13 +23,13 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "1.0.0"
+    version: "1.0.1"
   characters:
     dependency: transitive
     description:
       name: characters
       sha256: faf38497bda5ead2a8c7615f4f7939df04333478bf32e4173fcb06d428b5716b
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.4.1"
   clock:
@@ -37,7 +37,7 @@ packages:
     description:
       name: clock
       sha256: fddb70d9b5277016c77a80201021d40a2247104d9f4aa7bab7157b7e3f05b84b
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.1.2"
   collection:
@@ -45,7 +45,7 @@ packages:
     description:
       name: collection
       sha256: "2f5709ae4d3d59dd8f7cd309b4e023046b57d8a6c82130785d2b0e5868084e76"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.19.1"
   cupertino_icons:
@@ -53,7 +53,7 @@ packages:
     description:
       name: cupertino_icons
       sha256: "41e005c33bd814be4d3096aff55b1908d419fde52ca656c8c47719ec745873cd"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.0.9"
   fake_async:
@@ -61,7 +61,7 @@ packages:
     description:
       name: fake_async
       sha256: "5368f224a74523e8d2e7399ea1638b37aecfca824a3cc4dfdf77bf1fa905ac44"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.3.3"
   file:
@@ -69,7 +69,7 @@ packages:
     description:
       name: file
       sha256: a3b4f84adafef897088c160faf7dfffb7696046cb13ae90b508c2cbc95d3b8d4
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "7.0.1"
   flutter:
@@ -87,7 +87,7 @@ packages:
     description:
       name: flutter_lints
       sha256: "3105dc8492f6183fb076ccf1f351ac3d60564bff92e20bfc4af9cc1651f4e7e1"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "6.0.0"
   flutter_test:
@@ -110,7 +110,7 @@ packages:
     description:
       name: leak_tracker
       sha256: "33e2e26bdd85a0112ec15400c8cbffea70d0f9c3407491f672a2fad47915e2de"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "11.0.2"
   leak_tracker_flutter_testing:
@@ -118,7 +118,7 @@ packages:
     description:
       name: leak_tracker_flutter_testing
       sha256: "1dbc140bb5a23c75ea9c4811222756104fbcd1a27173f0c34ca01e16bea473c1"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "3.0.10"
   leak_tracker_testing:
@@ -126,7 +126,7 @@ packages:
     description:
       name: leak_tracker_testing
       sha256: "8d5a2d49f4a66b49744b23b018848400d23e54caf9463f4eb20df3eb8acb2eb1"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "3.0.2"
   lints:
@@ -134,7 +134,7 @@ packages:
     description:
       name: lints
       sha256: "12f842a479589fea194fe5c5a3095abc7be0c1f2ddfa9a0e76aed1dbd26a87df"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "6.1.0"
   matcher:
@@ -142,7 +142,7 @@ packages:
     description:
       name: matcher
       sha256: dc0b7dc7651697ea4ff3e69ef44b0407ea32c487a39fff6a4004fa585e901861
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.12.19"
   material_color_utilities:
@@ -150,23 +150,23 @@ packages:
     description:
       name: material_color_utilities
       sha256: "9c337007e82b1889149c82ed242ed1cb24a66044e30979c44912381e9be4c48b"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.13.0"
   meta:
     dependency: transitive
     description:
       name: meta
-      sha256: "23f08335362185a5ea2ad3a4e597f1375e78bce8a040df5c600c8d3552ef2394"
-      url: "https://pub.dev"
+      sha256: "1741988757a65eb6b36abe716829688cf01910bbf91c34354ff7ec1c3de2b349"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "1.17.0"
+    version: "1.18.0"
   path:
     dependency: transitive
     description:
       name: path
       sha256: "75cca69d1490965be98c73ceaea117e8a04dd21217b37b292c9ddbec0d955bc5"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.9.1"
   platform:
@@ -174,7 +174,7 @@ packages:
     description:
       name: platform
       sha256: "5d6b1b0036a5f331ebc77c850ebc8506cbc1e9416c27e59b439f917a902a4984"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "3.1.6"
   plugin_platform_interface:
@@ -182,7 +182,7 @@ packages:
     description:
       name: plugin_platform_interface
       sha256: "4820fbfdb9478b1ebae27888254d445073732dae3d6ea81f0b7e06d5dedc3f02"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.8"
   process:
@@ -190,7 +190,7 @@ packages:
     description:
       name: process
       sha256: c6248e4526673988586e8c00bb22a49210c258dc91df5227d5da9748ecf79744
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "5.0.5"
   sky_engine:
@@ -203,7 +203,7 @@ packages:
     description:
       name: source_span
       sha256: "56a02f1f4cd1a2d96303c0144c93bd6d909eea6bee6bf5a0e0b685edbd4c47ab"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.10.2"
   stack_trace:
@@ -211,7 +211,7 @@ packages:
     description:
       name: stack_trace
       sha256: "8b27215b45d22309b5cddda1aa2b19bdfec9df0e765f2de506401c071d38d1b1"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.12.1"
   stream_channel:
@@ -219,7 +219,7 @@ packages:
     description:
       name: stream_channel
       sha256: "969e04c80b8bcdf826f8f16579c7b14d780458bd97f56d107d3950fdbeef059d"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.1.4"
   string_scanner:
@@ -227,7 +227,7 @@ packages:
     description:
       name: string_scanner
       sha256: "921cd31725b72fe181906c6a94d987c78e3b98c2e205b397ea399d4054872b43"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.4.1"
   sync_http:
@@ -235,7 +235,7 @@ packages:
     description:
       name: sync_http
       sha256: "7f0cd72eca000d2e026bcd6f990b81d0ca06022ef4e32fb257b30d3d1014a961"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "0.3.1"
   term_glyph:
@@ -243,23 +243,23 @@ packages:
     description:
       name: term_glyph
       sha256: "7f554798625ea768a7518313e58f83891c7f5024f88e46e7182a4558850a4b8e"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "1.2.2"
   test_api:
     dependency: transitive
     description:
       name: test_api
-      sha256: "8161c84903fd860b26bfdefb7963b3f0b68fee7adea0f59ef805ecca346f0c7a"
-      url: "https://pub.dev"
+      sha256: "949a932224383300f01be9221c39180316445ecb8e7547f70a41a35bf421fb9e"
+      url: "https://pub.flutter-io.cn"
     source: hosted
-    version: "0.7.10"
+    version: "0.7.11"
   vector_math:
     dependency: transitive
     description:
       name: vector_math
       sha256: d530bd74fea330e6e364cda7a85019c434070188383e1cd8d9777ee586914c5b
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "2.2.0"
   vm_service:
@@ -267,7 +267,7 @@ packages:
     description:
       name: vm_service
       sha256: "0016aef94fc66495ac78af5859181e3f3bf2026bd8eecc72b9565601e19ab360"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "15.2.0"
   webdriver:
@@ -275,7 +275,7 @@ packages:
     description:
       name: webdriver
       sha256: "2f3a14ca026957870cfd9c635b83507e0e51d8091568e90129fbf805aba7cade"
-      url: "https://pub.dev"
+      url: "https://pub.flutter-io.cn"
     source: hosted
     version: "3.1.0"
 sdks:
diff --git a/lib/ch934x_serial.dart b/lib/ch934x_serial.dart
index 65cf7f7..99547cd 100644
--- a/lib/ch934x_serial.dart
+++ b/lib/ch934x_serial.dart
@@ -29,16 +29,14 @@ class Ch934xSerial {
   // ---------------------------------------------------------------------------
 
   /// 获取所有已连接的 CH934X 设备信息。
-  Future<List<Ch934xDeviceInfo>> getDeviceList() =>
-      _platform.getDeviceList();
+  Future<List<Ch934xDeviceInfo>> getDeviceList() => _platform.getDeviceList();
 
   /// 获取指定设备序列号;非 CH934X 设备时返回 null。
   Future<String?> getSerialNumber(int deviceId) =>
       _platform.getSerialNumber(deviceId);
 
   /// 获取指定设备类型,取值见 [Ch934xDeviceType]。
-  Future<int> getDeviceType(int deviceId) =>
-      _platform.getDeviceType(deviceId);
+  Future<int> getDeviceType(int deviceId) => _platform.getDeviceType(deviceId);
 
   /// 获取指定设备的串口列表。
   Future<List<Ch934xSerialPortInfo>> getSerialPortList(
@@ -85,7 +83,11 @@ class Ch934xSerial {
   Future<Uint8List> read(int length) => _platform.read(length);
 
   /// 写入数据,返回实际写入的字节数。
-  Future<int> write(Uint8List data) => _platform.write(data);
+  ///
+  /// [serialPortIndex] 为空时沿用当前活跃串口；传入时直接写入指定端口，
+  /// 不会改变当前活跃串口。
+  Future<int> write(Uint8List data, {int? serialPortIndex}) =>
+      _platform.write(data, serialPortIndex: serialPortIndex);
 
   /// 构造一个持续从串口拉取数据的 `Stream<Uint8List>`。
   ///
@@ -180,12 +182,10 @@ class Ch934xSerial {
   Future<int> getCurrentMode() => _platform.getCurrentMode();
 
   /// 获取 GPIO 数量。
-  Future<int> getGpiocount(int deviceId) =>
-      _platform.getGpiocount(deviceId);
+  Future<int> getGpiocount(int deviceId) => _platform.getGpiocount(deviceId);
 
   /// 获取 GPIO 组数。
-  Future<int> getGpiogroup(int deviceId) =>
-      _platform.getGpiogroup(deviceId);
+  Future<int> getGpiogroup(int deviceId) => _platform.getGpiogroup(deviceId);
 
   /// 使能 GPIO。
   Future<bool> enableGpio({
@@ -222,12 +222,10 @@ class Ch934xSerial {
       );
 
   /// 查询设备是否已打开。
-  Future<bool> isConnected(int deviceId) =>
-      _platform.isConnected(deviceId);
+  Future<bool> isConnected(int deviceId) => _platform.isConnected(deviceId);
 
   /// 获取当前已打开的设备 ID 列表。
-  Future<List<int>> getConnectedDevices() =>
-      _platform.getConnectedDevices();
+  Future<List<int>> getConnectedDevices() => _platform.getConnectedDevices();
 
   /// 配置当前活跃串口的参数。
   Future<bool> setSerialParameter({
diff --git a/lib/ch934x_serial_method_channel.dart b/lib/ch934x_serial_method_channel.dart
index b963bbf..9a2fdf9 100644
--- a/lib/ch934x_serial_method_channel.dart
+++ b/lib/ch934x_serial_method_channel.dart
@@ -14,8 +14,7 @@ import 'src/models/models.dart';
 class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
   /// 测试时可被替换的 MethodChannel。
   @visibleForTesting
-  final MethodChannel methodChannel =
-      const MethodChannel('ch934x_serial');
+  final MethodChannel methodChannel = const MethodChannel('ch934x_serial');
 
   /// 通知 Dart 侧的异常事件流,用于支持 `setExceptionCallback`。
   final StreamController<Ch934xException> _exceptionController =
@@ -39,7 +38,8 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
 
   @override
   Future<List<Ch934xDeviceInfo>> getDeviceList() async {
-    final raw = await methodChannel.invokeMethod<List<dynamic>>('getDeviceList');
+    final raw =
+        await methodChannel.invokeMethod<List<dynamic>>('getDeviceList');
     if (raw == null) {
       return const <Ch934xDeviceInfo>[];
     }
@@ -137,14 +137,15 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
   }
 
   @override
-  Future<int> write(Uint8List data) async {
-    if (data.isEmpty) {
+  Future<int> write(Uint8List data, {int? serialPortIndex}) async {
+    if (data.isEmpty || (serialPortIndex != null && serialPortIndex < 0)) {
       return 0;
     }
-    final result = await methodChannel.invokeMethod<int>(
-      'write',
-      <String, Object>{'data': data},
-    );
+    final args = <String, Object>{'data': data};
+    if (serialPortIndex != null) {
+      args['serialPortIndex'] = serialPortIndex;
+    }
+    final result = await methodChannel.invokeMethod<int>('write', args);
     return result ?? 0;
   }
 
@@ -225,7 +226,8 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
 
   @override
   Future<int> getCurrentMode() {
-    return methodChannel.invokeMethod<int>('getCurrentMode')
+    return methodChannel
+        .invokeMethod<int>('getCurrentMode')
         .then((v) => v ?? -1);
   }
 
@@ -301,7 +303,8 @@ class MethodChannelCh934xSerial extends Ch934xSerialPlatform {
 
   @override
   Future<List<int>> getConnectedDevices() async {
-    final raw = await methodChannel.invokeMethod<List<dynamic>>('getConnectedDevices');
+    final raw =
+        await methodChannel.invokeMethod<List<dynamic>>('getConnectedDevices');
     if (raw == null) return const <int>[];
     return raw.whereType<int>().toList(growable: false);
   }
diff --git a/lib/ch934x_serial_platform_interface.dart b/lib/ch934x_serial_platform_interface.dart
index ba0715d..e8b0896 100644
--- a/lib/ch934x_serial_platform_interface.dart
+++ b/lib/ch934x_serial_platform_interface.dart
@@ -79,7 +79,9 @@ abstract class Ch934xSerialPlatform extends PlatformInterface {
   Future<Uint8List> read(int length, {int? serialPortIndex});
 
   /// 向串口写入数据(对应 6.2.1 `UsbSerial.write`)。
-  Future<int> write(Uint8List data);
+  ///
+  /// [serialPortIndex] 为空时使用当前活跃端口；传入时直接写入指定端口。
+  Future<int> write(Uint8List data, {int? serialPortIndex});
 
   // ---------------------------------------------------------------------------
   // GPIO
diff --git a/pubspec.yaml b/pubspec.yaml
index f94ee49..6ce59f0 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: ch934x_serial
 description: "Flutter 插件,封装南京沁恒 CH934X 系列 USB 转串口芯片的 Android SDK,提供设备查找、串口读写、GPIO 与 Modem 控制等能力。"
-version: 1.0.0
+version: 1.0.1
 homepage: https://example.com/ch934x_serial
 
 environment:
diff --git a/test/ch934x_serial_method_channel_test.dart b/test/ch934x_serial_method_channel_test.dart
index 0d763a9..e74b841 100644
--- a/test/ch934x_serial_method_channel_test.dart
+++ b/test/ch934x_serial_method_channel_test.dart
@@ -69,13 +69,39 @@ void main() {
   test('write 将数据写入原生层并回传字节数', () async {
     mockCall((call) async {
       expect(call.method, 'write');
-      expect((call.arguments as Map)['data'], isA<Uint8List>());
+      expect(call.arguments, <String, Object>{
+        'data': Uint8List.fromList([9, 8, 7]),
+      });
       return 3;
     });
     final written = await platform.write(Uint8List.fromList([9, 8, 7]));
     expect(written, 3);
   });
 
+  test('write 透传显式串口索引', () async {
+    mockCall((call) async {
+      expect(call.method, 'write');
+      expect(call.arguments, <String, Object>{
+        'data': Uint8List.fromList([9, 8, 7]),
+        'serialPortIndex': 2,
+      });
+      return 3;
+    });
+    final written = await platform.write(
+      Uint8List.fromList([9, 8, 7]),
+      serialPortIndex: 2,
+    );
+    expect(written, 3);
+  });
+
+  test('write 接收负串口索引直接返回零', () async {
+    final written = await platform.write(
+      Uint8List.fromList([9]),
+      serialPortIndex: -1,
+    );
+    expect(written, 0);
+  });
+
   test('getModemStatus 默认回退到 0', () async {
     mockCall((_) async => null);
     expect(await platform.getModemStatus(), 0);
diff --git a/test/ch934x_serial_test.dart b/test/ch934x_serial_test.dart
index caf98c4..8d37f44 100644
--- a/test/ch934x_serial_test.dart
+++ b/test/ch934x_serial_test.dart
@@ -45,6 +45,7 @@ class _MockCh934xSerialPlatform extends Ch934xSerialPlatform
   bool closeResult;
   Uint8List? readBytes;
   int writeResult;
+  int? lastWritePort;
   bool gpioOutputResult;
   int gpioInput;
   bool modemControlResult;
@@ -63,8 +64,7 @@ class _MockCh934xSerialPlatform extends Ch934xSerialPlatform
   Future<List<Ch934xSerialPortInfo>> getSerialPortList(
     int deviceId, {
     required int interfaceNumber,
-  }) async =>
-      ports;
+  }) async => ports;
 
   @override
   Future<bool> openPort(Ch934xPortTarget target) async => openResult;
@@ -79,17 +79,20 @@ class _MockCh934xSerialPlatform extends Ch934xSerialPlatform
   Future<bool> requestUsbPermission(int deviceId) async => true;
 
   @override
-  Future<Uint8List> read(int length, {int? serialPortIndex}) async => readBytes ?? Uint8List(0);
+  Future<Uint8List> read(int length, {int? serialPortIndex}) async =>
+      readBytes ?? Uint8List(0);
 
   @override
-  Future<int> write(Uint8List data) async => writeResult;
+  Future<int> write(Uint8List data, {int? serialPortIndex}) async {
+    lastWritePort = serialPortIndex;
+    return writeResult;
+  }
 
   @override
   Future<bool> setGpioOutput({
     required int gpioNumber,
     required int level,
-  }) async =>
-      gpioOutputResult;
+  }) async => gpioOutputResult;
 
   @override
   Future<int> getGpioInput(int gpioNumber) async => gpioInput;
@@ -105,13 +108,19 @@ class _MockCh934xSerialPlatform extends Ch934xSerialPlatform
   Future<void> setExceptionCallback(
     void Function(Ch934xException exception) onException,
   ) async {}
+
+  @override
+  dynamic noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 }
 
 void main() {
   TestWidgetsFlutterBinding.ensureInitialized();
 
   test('默认平台实现是 MethodChannelCh934xSerial', () {
-    expect(Ch934xSerialPlatform.instance, isInstanceOf<MethodChannelCh934xSerial>());
+    expect(
+      Ch934xSerialPlatform.instance,
+      isInstanceOf<MethodChannelCh934xSerial>(),
+    );
   });
 
   test('Ch934xSerial 委托 platform 调用 getDeviceList', () async {
@@ -131,6 +140,20 @@ void main() {
     expect(list.single.serialNumber, 'SN-1');
   });
 
+  test('Ch934xSerial write 透传可选串口索引', () async {
+    final mock = _MockCh934xSerialPlatform(writeResult: 3);
+    final plugin = Ch934xSerial.withPlatform(mock);
+
+    expect(await plugin.write(Uint8List.fromList([1, 2, 3])), 3);
+    expect(mock.lastWritePort, isNull);
+
+    expect(
+      await plugin.write(Uint8List.fromList([1, 2, 3]), serialPortIndex: 4),
+      3,
+    );
+    expect(mock.lastWritePort, 4);
+  });
+
   test('ModemStatus.isSet 按位与工作', () {
     const status = ModemStatus.cts | ModemStatus.dcd;
     expect(ModemStatus.isSet(status, ModemStatus.cts), isTrue);