diff --git a/contract/Forest/ForestContract_Tree.cs b/contract/Forest/ForestContract_Tree.cs
index 6a6290b..12d1b46 100644
--- a/contract/Forest/ForestContract_Tree.cs
+++ b/contract/Forest/ForestContract_Tree.cs
@@ -69,6 +69,7 @@ public override Empty ClaimTreePoints(ClaimTreePointsInput input)
         CheckPointsRequestHash(requestStr, input.RequestHash);
         
         var lastOpTime = State.TreePointsActivityClaimTimeMap[input.Address][input.ActivityId];
+        Assert(lastOpTime == 0, "You have already participated in this activity");
         Assert(input.OpTime > lastOpTime, "Invalid param OpTime");
 
         var treePointsInfo = State.TreePointsMap[input.Address];