diff --git a/sec-beidou/src/main/java/com/imdroid/beidou/controller/CmdLineController.java b/sec-beidou/src/main/java/com/imdroid/beidou/controller/CmdLineController.java
index 5256783e..83ad807d 100644
--- a/sec-beidou/src/main/java/com/imdroid/beidou/controller/CmdLineController.java
+++ b/sec-beidou/src/main/java/com/imdroid/beidou/controller/CmdLineController.java
@@ -43,24 +43,24 @@ public class CmdLineController extends BasicController{
                             @RequestParam("device_id") String deviceId,
                             @RequestParam("cmd_type") int cmdType) {
         String sendCmd = cmd.replaceAll(" +","");
-        short len = (short) (sendCmd.length()/2);
+        short len = 0;
         int msgType;
         if(cmdType == 0){ // GNSS
             msgType = 0xD310;
-            len += 4;
+            len = (short) (sendCmd.length()/2+4);
             sendCmd = "D310"+ HexUtil.Short2HexString(len)+
                     HexUtil.Int2HexString(Integer.parseInt(deviceId))+sendCmd;
         }
         else if(cmdType == 1){ // DTU
             msgType = 0xD31A;
-            len += 5;
+            len = (short) (sendCmd.length() + 5);
             sendCmd = "D31A"+ HexUtil.Short2HexString(len)+
                     HexUtil.Int2HexString(Integer.parseInt(deviceId))+
                     "01"+HexUtil.String2HexString(sendCmd);
         }
         else {
             msgType = 0xD311;
-            len += 4;
+            len = (short) (sendCmd.length()/2+4);
             sendCmd = "D311"+ HexUtil.Short2HexString(len)+
                     HexUtil.Int2HexString(Integer.parseInt(deviceId))+sendCmd;
         }