In order to improve wet clutch's reliability, a parametric finite element model with the diameter of six outlet pipes as variables was established, and the heat-flow coupling analysis was carried out based on CFD. According to the characteristics of heat flow field, optimization strategy was designed. The sampling principle of CCD was analyzed, the formulas for the factorial coefficient, the number of sample points, the level and corresponding test times were deduced respectively, and applied to the response surface test design. Single factor simulation tests were adopted to determine the minimum axial displacement of clutch plates as the target variable, and test point arrangement table was further arranged. Based on least square method, the response surface model was fitted, three optimization schemes were obtained by different tools. The results show that, in the optimum scheme, the target variable increases by 38.472%, the error between forecast and actual simulation is 7.291%, and the thinnest oil-layer thickness increases by 18.828%.