diff --git a/Realtime/Realtime.Test/Throttle.cs b/Realtime/Realtime.Test/Throttle.cs
new file mode 100644
index 0000000..b0f5efa
--- /dev/null
+++ b/Realtime/Realtime.Test/Throttle.cs
@@ -0,0 +1,71 @@
+using NUnit.Framework;
+using System;
+using System.Threading.Tasks;
+using LeanCloud;
+using LeanCloud.Realtime;
+using LeanCloud.Realtime.Internal.Protocol;
+
+namespace Realtime.Test {
+    public class Throttle {
+        private LCIMClient c1;
+        private LCIMClient c2;
+
+        private LCIMConversation conversation;
+
+        [SetUp]
+        public async Task SetUp() {
+            LCLogger.LogDelegate += Utils.Print;
+            LCApplication.Initialize("ikGGdRE2YcVOemAaRbgp1xGJ-gzGzoHsz", "NUKmuRbdAhg1vrb2wexYo1jo", "https://ikggdre2.lc-cn-n1-shared.com");
+            c1 = new LCIMClient(Guid.NewGuid().ToString());
+            c2 = new LCIMClient(Guid.NewGuid().ToString());
+            await c1.Open();
+            await c2.Open();
+
+            conversation = await c1.CreateConversation(new string[] { Guid.NewGuid().ToString() });
+        }
+
+        [TearDown]
+        public async Task TearDown() {
+            await c1.Close();
+            await c2.Close();
+            LCLogger.LogDelegate -= Utils.Print;
+        }
+
+        [Test]
+        public void Equality() {
+            GenericCommand cmd1 = new GenericCommand {
+                Cmd = CommandType.Session,
+                Op = OpType.Open,
+                PeerId = "hello",
+                I = 1,
+                SessionMessage = new SessionCommand {
+                    Code = 123
+                }
+            };
+            GenericCommand cmd2 = new GenericCommand {
+                Cmd = CommandType.Session,
+                Op = OpType.Open,
+                PeerId = "hello",
+                I = 2,
+                SessionMessage = new SessionCommand {
+                    Code = 123
+                }
+            };
+            Assert.IsFalse(Equals(cmd1, cmd2));
+            cmd2.I = cmd1.I;
+            Assert.IsTrue(Equals(cmd1, cmd2));
+        }
+
+        [Test]
+        public async Task RemoveMemberTwice() {
+            Task t1 = conversation.RemoveMembers(new string[] { c2.Id }).ContinueWith(t => {
+                Assert.IsTrue(t.IsCompleted && !t.IsFaulted);
+            });
+            Task t2 = conversation.RemoveMembers(new string[] { c2.Id }).ContinueWith(t => {
+                Assert.IsTrue(t.IsCompleted && !t.IsFaulted);
+            });
+
+            await Task.WhenAll(t1, t2);
+        }
+    }
+}
diff --git a/Realtime/Realtime/Internal/Connection/LCConnection.cs b/Realtime/Realtime/Internal/Connection/LCConnection.cs
index 3b797ac..1e7732a 100644
--- a/Realtime/Realtime/Internal/Connection/LCConnection.cs
+++ b/Realtime/Realtime/Internal/Connection/LCConnection.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Linq;
 using System.Text;
 using System.Collections.Generic;
 using System.Threading.Tasks;
@@ -12,6 +13,17 @@ namespace LeanCloud.Realtime.Internal.Connection {
     /// 连接层，只与数据协议相关
     /// </summary>
     public class LCConnection {
+        // 请求/应答比对，即 I 相等
+        class RequestAndResponseComparer : IEqualityComparer<GenericCommand> {
+            public bool Equals(GenericCommand x, GenericCommand y) {
+                return true;
+            }
+
+            public int GetHashCode(GenericCommand obj) {
+                return obj.I;
+            }
+        }
+
         /// <summary>
         /// 连接状态
         /// </summary>
@@ -59,7 +71,7 @@ namespace LeanCloud.Realtime.Internal.Connection {
         /// <summary>
         /// 请求回调缓存
         /// </summary>
-        private readonly Dictionary<int, TaskCompletionSource<GenericCommand>> responses;
+        private readonly Dictionary<GenericCommand, TaskCompletionSource<GenericCommand>> requestToResponses;
 
         private int requestI = 1;
 
@@ -78,7 +90,8 @@ namespace LeanCloud.Realtime.Internal.Connection {
 
         internal LCConnection(string id) {
             this.id = id;
-            responses = new Dictionary<int, TaskCompletionSource<GenericCommand>>();
+            requestToResponses = new Dictionary<GenericCommand, TaskCompletionSource<GenericCommand>>(new RequestAndResponseComparer());
+
             heartBeat = new LCHeartBeat(this, OnDisconnect);
             router = new LCRTMRouter();
             ws = new LCWebSocketClient {
@@ -127,9 +140,24 @@ namespace LeanCloud.Realtime.Internal.Connection {
         /// <param name="request"></param>
         /// <returns></returns>
         internal async Task<GenericCommand> SendRequest(GenericCommand request) {
+            if (IsIdempotentCommand(request)) {
+                GenericCommand sendingReq = requestToResponses.Keys.FirstOrDefault(item => {
+                    // TRICK 除了 I 其他字段相等
+                    request.I = item.I;
+                    return Equals(request, item);
+                });
+                if (sendingReq != null) {
+                    LCLogger.Warn("duplicated request");
+                    if (requestToResponses.TryGetValue(sendingReq, out TaskCompletionSource<GenericCommand> waitingTcs)) {
+                        return await waitingTcs.Task;
+                    }
+                    LCLogger.Error($"error request: {request}");
+                }
+            }
+
             TaskCompletionSource<GenericCommand> tcs = new TaskCompletionSource<GenericCommand>();
             request.I = requestI++;
-            responses.Add(request.I, tcs);
+            requestToResponses.Add(request, tcs);
             try {
                 await SendCommand(request);
             } catch (Exception e) {
@@ -177,7 +205,7 @@ namespace LeanCloud.Realtime.Internal.Connection {
                 if (command.HasI) {
                     // 应答
                     int requestIndex = command.I;
-                    if (responses.TryGetValue(requestIndex, out TaskCompletionSource<GenericCommand> tcs)) {
+                    if (requestToResponses.TryGetValue(command, out TaskCompletionSource<GenericCommand> tcs)) {
                         if (command.HasErrorMessage) {
                             // 错误
                             ErrorCommand error = command.ErrorMessage;
@@ -189,7 +217,7 @@ namespace LeanCloud.Realtime.Internal.Connection {
                         } else {
                             tcs.TrySetResult(command);
                         }
-                        responses.Remove(requestIndex);
+                        requestToResponses.Remove(command);
                     } else {
                         LCLogger.Error($"No request for {requestIndex}");
                     }
@@ -303,5 +331,16 @@ namespace LeanCloud.Realtime.Internal.Connection {
         internal void Resume() {
             _ = Reconnect();
         }
+
+        private static bool IsIdempotentCommand(GenericCommand command) {
+            return !(
+                command.Cmd == CommandType.Direct ||
+                (command.Cmd == CommandType.Session && command.Op == OpType.Open) ||
+                (command.Cmd == CommandType.Conv &&
+                (command.Op == OpType.Start ||
+                command.Op == OpType.Update ||
+                command.Op == OpType.Members))
+            );
+        }
     }
 }