diff --git a/src/server/ltp_server.cpp b/src/server/ltp_server.cpp
index d15e6c29d..d61d04588 100644
--- a/src/server/ltp_server.cpp
+++ b/src/server/ltp_server.cpp
@@ -107,11 +107,17 @@ static int Service(struct mg_connection *conn) {
     string strSentence = sentence;
 
     // validation check
-    if (strlen(sentence) == 0 || !isclear(strSentence)) {
+    if (strlen(sentence) == 0) {
+      WARNING_LOG("Input sentence is empty");
+      std::string response = "HTTP/1.1 400 Empty sentence\r\n\r\n";
+      mg_printf(conn, "%s", response.c_str());
+      return 0;
+    }
+
+    if (!isclear(strSentence)) {
       WARNING_LOG("Failed string validation check");
       // Input sentence is not clear
-      std::string response = "HTTP/1.1 400 Bad Request\r\n\r\n";
-      response += "Input string not well formated";
+      std::string response = "HTTP/1.1 400 Encoding not in UTF8\r\n\r\n";
       mg_printf(conn, "%s", response.c_str());
       return 0;
     }
@@ -138,7 +144,7 @@ static int Service(struct mg_connection *conn) {
     if(str_xml == "y") {
       if (-1 == xml4nlp.LoadXMLFromString(strSentence)) {
         // Failed the xml validation check
-        std::string response = "HTTP/1.1 400 Bad Request\r\n\r\n";
+        std::string response = "HTTP/1.1 400 Bad XML format\r\n\r\n";
         response += "Failed to load custom xml";
         mg_printf(conn, "%s", response.c_str());
         return 0;
@@ -175,9 +181,6 @@ static int Service(struct mg_connection *conn) {
 
     xml4nlp.ClearDOM();
   }
-
-  std::string response = "HTTP/1.1 500 Internal Server Error\r\n\r\n";
-  mg_printf(conn, "%s", response.c_str());
   return 1;
 }