diff --git a/fec_manager.cpp b/fec_manager.cpp
index 18b54d6..6fe167f 100644
--- a/fec_manager.cpp
+++ b/fec_manager.cpp
@@ -16,7 +16,7 @@ int g_fec_redundant_num=10;
 int g_fec_mtu=1250;
 int g_fec_queue_len=200;
 int g_fec_timeout=8*1000; //8ms
-int g_fec_mode=1;
+int g_fec_mode=0;
 
 int dynamic_update_fec=1;
 
diff --git a/main.cpp b/main.cpp
index ec1f622..4839d0e 100644
--- a/main.cpp
+++ b/main.cpp
@@ -34,19 +34,22 @@ static void print_help()
 	printf("main options:\n");
 	printf("    -f,--fec              x:y             forward error correction, send y redundant packets for every x packets\n");
 	printf("    --timeout             <number>        how long could a packet be held in queue before doing fec, unit: ms, default: 8ms\n");
-	printf("    --mode                <number>        fec-mode,available values: 0, 1; 0 cost less bandwidth, 1 cost less latency(default)\n");
 	printf("    --report              <number>        turn on send/recv report, and set a period for reporting, unit: s\n");
 
 	printf("advanced options:\n");
-	printf("    --mtu                 <number>        mtu. for mode 0, the program will split packet to segment smaller than mtu_value.\n");
+	printf("    --mode                <number>        fec-mode,available values: 0,1; mode 0(default) costs less bandwidth,no mtu problem.\n");
+	printf("                                          mode 1 usually introduces less latency, but you have to care about mtu.\n");
+	printf("    --mtu                 <number>        mtu. for mode 0, the program will split packet to segment smaller than mtu value.\n");
 	printf("                                          for mode 1, no packet will be split, the program just check if the mtu is exceed.\n");
-	printf("                                          default value: 1250\n");
+	printf("                                          default value: 1250. you typically shouldnt change this value.\n");
+    printf("    -q,--queue-len        <number>        fec queue len, only for mode 0, fec will be performed immediately after queue is full.\n");
+	printf("                                          default value: 200. \n");
 	printf("    -j,--jitter           <number>        simulated jitter. randomly delay first packet for 0~<number> ms, default value: 0.\n");
 	printf("                                          do not use if you dont know what it means.\n");
 	printf("    -i,--interval         <number>        scatter each fec group to a interval of <number> ms, to protect burst packet loss.\n");
 	printf("                                          default value: 0. do not use if you dont know what it means.\n");
-	printf("    --random-drop         <number>        simulate packet loss, unit: 0.01%%. default value: 0\n");
-	printf("    --disable-obscure     <number>        disable obscure, to save a bit bandwidth and cpu\n");
+	printf("    --random-drop         <number>        simulate packet loss, unit: 0.01%%. default value: 0.\n");
+	printf("    --disable-obscure     <number>        disable obscure, to save a bit bandwidth and cpu.\n");
 //	printf("    --disable-xor         <number>        disable xor\n");
 
 	printf("developer options:\n");
@@ -55,7 +58,6 @@ static void print_help()
 	printf("                                          supported commands.\n");
 	printf("    -j ,--jitter          jmin:jmax       similiar to -j above, but create jitter randomly between jmin and jmax\n");
 	printf("    -i,--interval         imin:imax       similiar to -i above, but scatter randomly between imin and imax\n");
-    printf("    -q,--queue-len        <number>        max fec queue len, only for mode 0\n");
     printf("    --decode-buf          <number>        size of buffer of fec decoder,u nit: packet, default: 2000\n");
     printf("    --fix-latency         <number>        try to stabilize latency, only for mode 0\n");
     printf("    --delay-capacity      <number>        max number of delayed packets\n");