diff --git a/service/devicedebug/devicedebug_main.c b/service/devicedebug/devicedebug_main.c
index 5aa22a9c..72e64497 100644
--- a/service/devicedebug/devicedebug_main.c
+++ b/service/devicedebug/devicedebug_main.c
@@ -38,7 +38,7 @@ APPSPAWN_STATIC int DeviceDebugShowHelp(int argc, char *argv[])
     printf("\r\nusage: devicedebug <command> <options>\r\n"
         "\r\nThese are common devicedebug commands list:\r\n"
         "\r\n         help              list available commands"
-        "\r\n         kill              send a signal to a process\r\n");
+        "\r\n         kill              send a signal(1-64) to a process\r\n");
 
     return 0;
 }
@@ -76,7 +76,9 @@ int main(int argc, char *argv[])
     /* 检验用户命令，获取对应的处理函数 */
     cmdInfo = DeviceDebugCmdCheck(argv[DEVICEDEBUG_NUM_1]);
     if (cmdInfo == NULL) {
-        DEVICEDEBUG_LOGE("invalid cmd!. cmd:%{public}s\r\n", argv[DEVICEDEBUG_NUM_1]);
+        printf("devicedebug: '%s' is not a valid devicedebug command. See 'devicedebug help'.",
+            argv[DEVICEDEBUG_NUM_1]);
+        DeviceDebugShowHelp(argc, argv);
         return DEVICEDEBUG_ERRNO_OPERATOR_TYPE_INVALID;
     }
 
diff --git a/service/devicedebug/kill/src/devicedebug_kill.c b/service/devicedebug/kill/src/devicedebug_kill.c
index f36c177f..08be2ee9 100644
--- a/service/devicedebug/kill/src/devicedebug_kill.c
+++ b/service/devicedebug/kill/src/devicedebug_kill.c
@@ -36,7 +36,7 @@ APPSPAWN_STATIC void DeviceDebugShowKillHelp(void)
     printf("\r\nusage: devicedebug kill [options] <pid>"
         "\r\noptions list:"
         "\r\n         -h, --help                list available commands"
-        "\r\n         kill -<signal> <pid>      send a signal to a process\r\n");
+        "\r\n         kill -<signal> <pid>      send a signal(1-64) to a process\r\n");
 }
 
 APPSPAWN_STATIC char* DeviceDebugJsonStringGeneral(int pid, const char *op, cJSON *args)
@@ -133,7 +133,7 @@ int DeviceDebugCmdKill(int argc, char *argv[])
 
     int signal = atoi(argv[DEVICEDEBUG_KILL_CMD_SIGNAL_INDEX] + 1);
     if (signal > SIGRTMAX || signal <= 0) {
-        DEVICEDEBUG_LOGE("signal is %{public}d > %{public}d", signal, SIGRTMAX);
+        DEVICEDEBUG_LOGE("signal is %{public}d not in [1, %{public}d]", signal, SIGRTMAX);
         DeviceDebugShowKillHelp();
         return DEVICEDEBUG_ERRNO_PARAM_INVALID;
     }