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 038fec90..cded5c89 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
@@ -38,19 +38,11 @@ public class Gga {
     public Gga() {
     }
 
-    static public Gga getFrom(ByteBuf data){
+    public static Gga getFrom(ByteBuf data){
         int msgFlag = data.getUnsignedShort(0);
-        if(msgFlag == 0xD341){
-            return getFromD341(data);
+        if(msgFlag != 0xD341 && msgFlag != 0xD331){
+            return null;
         }
-        else if(msgFlag == 0xD331){
-            return getFromD331(data);
-        }
-        else return null;
-
-    }
-
-    static Gga getFromD331(ByteBuf data){
         int pos = 26; // 从惯导之后开始
         boolean found = false;
         while(pos<data.readableBytes()){
@@ -65,29 +57,14 @@ public class Gga {
                     pos += 26;
                 }
                 else {
-                    pos++;
-                    pos += data.getUnsignedShort(pos) + 5;//length+payload+crc
-                }
-            }
-            else{
-                break;
-            }
-        }
-        if(found){
-            return getFromGGAString(data, pos);
-        }
-        else return null;
-    }
+                    // +----------+----------+----------+
+                    // |    d3    |  6bit |   10bits    |
+                    // +----------+----------+----------+
+                    // d3 xx payload len(10bits)
 
-    static Gga getFromD341(ByteBuf data){
-        int pos = 26; // 从惯导之后开始
-        boolean found = false;
-        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;
+                    pos++;
+                    pos += ((data.getUnsignedShort(pos)&0x03FF) + 5);//length(2byte)+payload+crc(3byte)
+                }
             }
             else if(b562_flag[0] == d0 && b562_flag[1] == d1){
                 pos += 4; // type, class id