In order to improve the braking torque coefficient, the numerical simulation of 3D transient multiphase flow was performed to the turbulent flow in Hydraulic Retarder. By the analysis of internal flow field characteristics, both the flow separation phenomenon in the work flow channel and the vortex generated in the chord surface went against the output of the braking torque. To solve this problem, considering correlation between the structural parameters of hydraulic retarder, numerical analysis based on multi-parameter flow field was performed, and the blade cascade parameters were optimized. The results showed that, the method through the analysis of the multi-parameter flow field to optimize blade cascade parameters was reasonable. When the blade angle and chamfer angle were optimized, the vortex and the flow separation phenomenon in the flow channel of impeller disappeared and the braking torque coefficient increased by 6%. 