diff --git a/webapp/services/FormulaService.php b/webapp/services/FormulaService.php
index 976ea568..d48fb7c1 100644
--- a/webapp/services/FormulaService.php
+++ b/webapp/services/FormulaService.php
@@ -166,7 +166,7 @@ class FormulaService extends BaseService {
 
         $heroProbability = min($heroFragmentNum / $onlineNum *
                                $dropRate * ($instanceRankRate + $bossReward*0.2) *
-                               pow(2, $todayPveBattleTimes - $todayPveGetFragmentNum - 1), 1);
+                               pow(2, $todayPveBattleTimes - $todayPveLastGetFragmentBattle - 1), 1);
         error_log(json_encode(func_get_args()));
         return max(0, $heroProbability);
     }