The Hanzhuang line and twin-lane locks use the same lower approach channel and produce complex unsteady flow in filling and draining water.To ensure that the ships’ safe sailing and berthing,we probe into the complex unsteady flow of lower approach channel in different upstream and downstream level combinations by MIKE21 hydrodynamic model,simulating the distribution of the longitudinal velocity,the lateral velocity and the circulation flow.The result shows that Hanzhuang line and the twin-lane locks don’t meet the navigation requirements during the flood period.In view of the hydraulics problems of flood period,we put forward the effective engineering measures using grille and local dredging.