diff --git a/SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/DebugAgent.c b/SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/DebugAgent.c
index 239cf63f6b..91b29af82a 100644
--- a/SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/DebugAgent.c
+++ b/SourceLevelDebugPkg/Library/DebugAgent/DebugAgentCommon/DebugAgent.c
@@ -374,6 +374,7 @@ UpdateMailboxContent (
     Mailbox->SequenceNo = (UINT8) Value;
     break;
   case DEBUG_MAILBOX_HOST_SEQUENCE_NO_INDEX:
+    DebugAgentMsgPrint (DEBUG_AGENT_INFO, "Update HostSequenceNo to %x\n", Value);
     Mailbox->ToBeCheckSum = Mailbox->CheckSum + CalculateSum8 ((UINT8 *)&Mailbox->HostSequenceNo, sizeof(UINT8))
                                               - CalculateSum8 ((UINT8 *)&Value, sizeof(UINT8));
     Mailbox->HostSequenceNo = (UINT8) Value;
@@ -572,6 +573,7 @@ DebugAgentDataMsgPrint (
   @retval EFI_SUCCESS        Read the symbol in BreakSymbol.
   @retval EFI_CRC_ERROR      CRC check fail.
   @retval EFI_TIMEOUT        Timeout occurs when reading debug packet.
+  @retval EFI_DEVICE_ERROR   Receive the old or responsed packet.
 
 **/
 EFI_STATUS
@@ -581,6 +583,8 @@ ReadRemainingBreakPacket (
   )
 {
   UINT16                     Crc;
+  DEBUG_AGENT_MAILBOX        *Mailbox;
+
   //
   // Has received start symbol, try to read the rest part
   //
@@ -599,9 +603,20 @@ ReadRemainingBreakPacket (
     DebugAgentDataMsgPrint (DEBUG_AGENT_VERBOSE, FALSE, (UINT8 *)DebugHeader, DebugHeader->Length);
     return EFI_CRC_ERROR;
   }
-
-  UpdateMailboxContent (GetMailboxPointer(), DEBUG_MAILBOX_HOST_SEQUENCE_NO_INDEX, DebugHeader->SequenceNo);
-  return EFI_SUCCESS;
+  Mailbox = GetMailboxPointer();
+  if (((DebugHeader->Command & DEBUG_COMMAND_RESPONSE) != 0) &&
+       (DebugHeader->SequenceNo == (UINT8) (Mailbox->HostSequenceNo + 1))) {
+    //
+    // Only updagte HostSequenceNo for new command packet 
+    //
+    UpdateMailboxContent (Mailbox, DEBUG_MAILBOX_HOST_SEQUENCE_NO_INDEX, DebugHeader->SequenceNo);
+    return EFI_SUCCESS;
+  } else {
+    //
+    // If one old command or response packet received, skip it
+    //
+    return EFI_DEVICE_ERROR;
+  }
 }
 
 /**