diff --git a/server/light_backtask/task/chain_activity.go b/server/light_backtask/task/chain_activity.go
index 2b19a68b..e8207bc5 100644
--- a/server/light_backtask/task/chain_activity.go
+++ b/server/light_backtask/task/chain_activity.go
@@ -143,8 +143,8 @@ func (this* chainActivity) saveToDb(ds *f5.DataSet) bool {
 		}
 	} else if eventName == "UnLock" {
 		p := new(unLockReturnValues)
-		sender := q5.SafeToString(p.User)
 		if q5.DecodeJson(returnValues, p) == nil {
+			sender := q5.SafeToString(p.User)
 			decodeJsonOk = true
 			for _, nft := range p.NftList {
 				if len(nft) != 3 {