A parametric matching optimization design method is proposed for plug-in hybrid vehicles equipped with the reflux power coupling transmission system. The equivalent input power model for each mode of thevehicle is established. Based on the principle of minimum equivalent input power, the switching rules between different driving modes are established, and the control parameter coefficients are set to adjust the mode switching curve. The economic simulation model of the whole vehicle is built by MATLAB/SIMULINK, and the matching dynamic parameters and control parameter coefficients are optimized by genetic algorithm. The simulation results show that the set of parameters obtained by this method can improve fuel economy effectively, and the equivalent fuel consumption per 100 km is reduced by 4.8% after optimization.