Water hydraulic servo valve has become an important research subject nowadays, and its secondary amplifier usually uses slide valve. Research on flow characteristics of water hydraulic slide valve is important to the design of water hydraulic servo valve. Based on the classical theory of incompressible flow, CFD software FLUENT is used to simulate and analyze the flow characteristics of water hydraulic slide valve. Simulations with different boundary values are applied to the same slide valve in order to guarantee the accuracy of the simulation results. Detailed comparisons are made between throttles with different structure parameters, including spool diameter, spool opening, flow passage diameter and equalizing slots so as to define the parameters respectively. The results indicate that the flow rate of the slide valve designed is approximately proportional to the spool opening within certain travel. Finally, the structure parameters of the slide valve that satisfy the design requirements are obtained. The simulation results provide theoretical basis for the design and improvement of water hydraulic slide valve used in water hydraulic servo valve.