diff --git a/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/bd/Gga.java b/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/bd/Gga.java
index 531899a5..2cf1e801 100644
--- a/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/bd/Gga.java
+++ b/sec-beidou-rtcm/src/main/java/com/imdroid/sideslope/bd/Gga.java
@@ -9,7 +9,7 @@ import java.nio.charset.Charset;
 public class Gga {
     public static int FIX_RESULT = 4;
     public static int FLOAT_RESULT = 5;
-    final static byte[] GGA_FLAG =  {'$', 'G'};//$xxGGA
+    final static byte[] GGA_FLAG =  {'$', 'X', 'X', 'G', 'G', 'A'};//$xxGGA
 
     final static byte[] d331_flag = {(byte) 0xd3, (byte)0x31};
     final static byte rtcm_flag = (byte)0xd3;
@@ -50,9 +50,14 @@ public class Gga {
         while(pos<data.readableBytes()){
             byte d0 = data.getByte(pos);
             byte d1 = data.getByte(pos+1);
-            if(GGA_FLAG[0] == d0 && GGA_FLAG[1] == d1){
-                found = true;
-                break;
+            if(GGA_FLAG[0] == d0){
+                if(data.readableBytes()>5 &&
+                        data.getByte(pos+3) == GGA_FLAG[3] &&
+                        data.getByte(pos+4) == GGA_FLAG[4] &&
+                        data.getByte(pos+5) == GGA_FLAG[5]) {
+                    found = true;
+                    break;
+                }
             }
             else if(d0 == rtcm_flag){
                 if(d1 == 0x31) { // d331粘包