The original steel sheet pile longitudinal cofferdam downstream of Gezhouba is a temporary facility and has now exceeded its service period.This paper studies the impact of steel sheet pile cofferdam on the navigation safety of the ship lock No.1，providing a basis for the demolition or reconstruction of steel sheet pile cofferdam.A two-dimensional hydrodynamic model is established for the downstream channel of Gezhouba Dam，and numerical simulation calculations are conducted for the demolition and reconstruction of steel sheet pile cofferdams under the maximum navigable flow of 35，000 m3/s at the Ship lock No.1.The calculation results show that when the diversion ratio of the two rivers is less than 0.9 and the smaller，the demolition of the steel sheet pile cofferdam has a greater impact on the navigation flow conditions in the downstream entrance area of the ship lock No.1.