Abstract: The hydrodynamic characteristics of the single-leaf gate of a high-head navigation lock located at a mountain river are studied in this paper. The submerged water depth of this gate is up to 30 meters. The dynamic simulation of the 3D unsteady flow field during the opening and closing processes of the single-leaf gate is made by using a Realizable k-ε turbulence model on the basis of FLUENT software. The three-dimensional flow field simulation of the whole processes of the gate opening and closing is realized by the aid of 3D prism grids stretched by the 2D hybrid grids, combined with the 2.5D reconstruction and elastic dynamic grid fairing method, reducing the number of grids and improving the efficiency of numerical simulation. The flow pattern around the gate, water level difference between the gate's front and back and the variation law of the hydraulic resisting torque are obtained by introducing the volume of fluid method (VOF) for the water-air two-phase flow into the iteration of calculation. The calculated results coincide well with the test results, which shows that the numerical model is reliable and has a high precision. It is found from the results of numerical solution that the values of the hydraulic resisting torque are influenced by the bottom clearance of the gate during its whole opening and closing processes and the peak value of the hydraulic torque decreases with the increase of the bottom clearance. The simulated results will help to optimize the design of gate structures and reduce the force of the directly-connected hydraulic hoist.