The invention relates to a numerical simulation method of hydrodynamic resistance torque when in opening and closing of a straight gate of a navigation lock, belonging to the technical field of navigation lock hydraulics. Based on an FLUENT fluid computation platform, the opening and closing dynamic process of the straight gate is controlled by virtue of a User-Defined Function (UDF), and numerical simulation of the hydrodynamic resistance torque in the opening and closing dynamic process of the straight gate is realized through establishing a three-dimensional mathematical model of the straight gate of the navigation lock, a gate chamber region and a lock chamber. The numerical simulation method proposed by the invention has the advantages that the accuracy is good, the possibility of fast and conveniently acquiring the hydrodynamic resistance torque when in opening and closing of the straight gate of the navigation lock can be provided, the numerical simulation method can be applied to determination of the hydrodynamic resistance torque of the straight gate of the navigation lock, determination of opening and closing force, design of capacity of a hoist, optimization of boundary conditions of a gate chamber, and the like, and the problems existing in test and study means of a physical model of time and energy waste, and the like can be solved.