Longweizhou Project will be constructed by the method of stage diversion.The first-stage cofferdam surrounds the eight-hole spillway gate and fishway,and utilizes the point bar to excavate the diversion channel.The second-stage cofferdam surrounds the ship lock,and utilizes the eight-hole spillway gate for diversion.To satisfy the navigable flow conditions during the operation period,the point bar cutting and channel dredging works are implemented simultaneously.This paper adopts numerical simulation to explore the surface water level variation caused by the implementation of cofferdam during construction period,channel dredging,beach cutting and operation of Longweizhou Junction.The results show that the first-stage and second-stage cofferdam cause the upstream surface water level to increase 0.28 and 0.20 m,and the downstream water level to decrease 0.08 m and 0.12 m,respectively,and the transverse gradient of water level in the upper section of the cofferdam is large.The channel dredging and point bar cutting work can effectively expand the channel section area and increase the channel storage capacity,which leads to the obvious fall of surface water level,and weakens the backwater caused by Longweizhou Project.