Using transactions data for A-Share stocks in Shanghai stock market,this paper studies the effect of the opening call auction which changes from closecall auction to open-call auction on market liquidity by using Event study methodology.This paper adopts panel data regression to test the change of the ratio of trading volume in the opening call auction market and the bid-ask spread,market depth,liquidity ratio and resiliency in the continuous auction market after the transparency of opening auction increased.The results indicate that the enthusiasm of the traders participating in opening auction is enhanced and market liquidity within 15 minutes after continuous trading is dramatically reduced in the open-call auction market.Based on the fact that different trades respond differently to the disclosed information,we conclude that the open-call auction can not only attract more traders to participate in opening auction,which may increase the validity of opening price,but also mitigate the traders' excess reflection on the opening information.