diff --git a/vnpy/trader/vtObject.py b/vnpy/trader/vtObject.py
index 966be5fe..d7a1d384 100644
--- a/vnpy/trader/vtObject.py
+++ b/vnpy/trader/vtObject.py
@@ -99,7 +99,8 @@ class VtBarData(VtBaseData):
         self.datetime = None                # python的datetime时间对象
         
         self.volume = EMPTY_INT             # 成交量
-        self.openInterest = EMPTY_INT       # 持仓量    
+        self.openInterest = EMPTY_INT       # 持仓量  
+        self.interval = EMPTY_UNICODE       # K线周期
     
 
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