To optimize the parameters of blade numbers of vehicular hydraulic retarder, a 3-D integrated optimization platform was established. The brake torque of hydraulic retarder was calculated with CFD solver and DOE technique of design variable. With DOE results, the RSM model was built to get the optimum parameters. The relationship of internal flow field and brake performance with the varying blade numbers was analyzed and concluded. Comparison of experimental data and simulation results before and after the optimization showed that the brake performance of hydraulic retarder with the optimum parameters was improved observably, and the 3-D integrated optimization platform was accurate and reliable.