The maximum design head of the second line ship lock of the Wan’an project is 32.5 m. In view of the shape of the back corridor of the valve in the water conveyance system of the high head lock，two schemes of gradual expansion at the top + flat bottom and sudden expansion at the top + sudden expansion at the bottom are compared and studied. The hydraulic model test and the unsteady flow atmospheric pressure test of valve corridor are used to compare and select the hydraulic characteristics，flow state and uniformity of flow，and the influence of pressure characteristics of sluice chamber. The results show that the top sudden expansion + bottom sudden expansion corridor is better than the top gradual expansion+flat bottom corridor in shortening water delivery time，improving the flow pattern of main gallery and inlet，reducing the pressure fluctuation，and cavitation of lower maintenance gate slot.