diff --git a/src/main/java/org/luyu/sdk/caller/LuyuSDK.java b/src/main/java/org/luyu/sdk/caller/LuyuSDK.java
index 0e895bf400c176c7e3182994c8d0a092241f07c4..209ffc504dc33f524678cb60cd8ba8ed694d0c9d 100644
--- a/src/main/java/org/luyu/sdk/caller/LuyuSDK.java
+++ b/src/main/java/org/luyu/sdk/caller/LuyuSDK.java
@@ -26,7 +26,9 @@ public class LuyuSDK extends ExtendSDK implements SDK {
     @Override
     public RemoteCall<Receipt> sendTransaction(Transaction tx) {
         // set nonce & version
-        tx.setNonce(NonceUtls.newNonce());
+        if (tx.getNonce() == 0) {
+            tx.setNonce(NonceUtls.newNonce());
+        }
         tx.setSender(account.getIdentity());
 
         // sign
diff --git a/src/main/java/org/luyu/sdk/utils/NonceUtls.java b/src/main/java/org/luyu/sdk/utils/NonceUtls.java
index 0ec11c6e89bac62afb4de0cc0f610689a6ab3b5e..c9390a1cbad7d2bef838d466aecd784a326d4df9 100644
--- a/src/main/java/org/luyu/sdk/utils/NonceUtls.java
+++ b/src/main/java/org/luyu/sdk/utils/NonceUtls.java
@@ -6,6 +6,10 @@ public class NonceUtls {
     private static final SecureRandom rand = new SecureRandom();
 
     public static synchronized long newNonce() {
-        return rand.nextLong();
+        long n = rand.nextLong();
+        if (n < 0) {
+            n &= Long.MAX_VALUE;
+        }
+        return n;
     }
 }