In Yuandong ship lock expansion project,we establish a physical model of 1：40 scale ratio to study the long wave movement,water surface slope,velocity distribution,and backflow intensity when the lock empties and afterwards.The results show that the reverse water head at the miter gate is 0.39 m,and the longitudinal surface velocity at the mooring site is 0.62 m/s under the designed condition.These values are beyond relevant standards,so measures shall be taken to improve the navigation condition.