diff --git a/qlib/contrib/backtest/account.py b/qlib/contrib/backtest/account.py
index a614f08b6..b2e307fe5 100644
--- a/qlib/contrib/backtest/account.py
+++ b/qlib/contrib/backtest/account.py
@@ -167,3 +167,4 @@ class Account:
     def save_account(self, account_path):
         self.current.save_position(account_path / "position.xlsx", self.last_trade_date)
         self.report.save_report(account_path / "report.csv")
+
diff --git a/qlib/contrib/backtest/exchange.py b/qlib/contrib/backtest/exchange.py
index cbb3d7932..369b3aef3 100644
--- a/qlib/contrib/backtest/exchange.py
+++ b/qlib/contrib/backtest/exchange.py
@@ -93,7 +93,7 @@ class Exchange:
         self.limit_threshold = limit_threshold
         # TODO: the quote, trade_dates, codes are not necessray.
         # It is just for performance consideration.
-        if trade_dates is not None and trade_dates:
+        if trade_dates is not None and len(trade_dates):
             start_date, end_date = trade_dates[0], trade_dates[-1]
         else:
             self.logger.warning("trade_dates have not been assigned, all dates will be loaded")
@@ -325,7 +325,7 @@ class Exchange:
             deal_amount = self.get_real_deal_amount(current_amount, target_amount, factor)
             if deal_amount == 0:
                 continue
-            if deal_amount > 0:
+            elif deal_amount > 0:
                 # buy stock
                 buy_order_list.append(
                     Order(
@@ -423,3 +423,4 @@ class Exchange:
             raise NotImplementedError("order type {} error".format(order.type))
 
         return trade_val, trade_cost
+