Abstract: The selection about culvert shape behind valve is one of the key problems in hydraulic design for Three Gorges ship lock.Comparisons of hydraulic natures such as flow pattern,pressure fluctuation,cavitation,and vibration between two kinds of culvert shape behind valve,top expansion and bottom sudden expansion,are carried out in this paper.Due to the obvious difference,bottom sudden expansion culvert is used in Three Gorges ship lock,which can fulfill the operating conditions of filling valve.