According to single-motor plug-in hybrid electric vehicle with Continuous Variable Transmission (CVT), a novel design method of power and control parameters was proposed. The system efficiency model for each mode of Plug-in Hybrid Electric Vehicl (PHEV) was built, the mode switching rules based on system efficiency was then obtained, and the adjustment of the mode switching rules through multiplying the mode switching curve with control parameters was realized. Fully considering the influencing factors of fuel economy, the power source, battery number and final drive ratio were regarded as the power parameters. By using Matlab/Simulink, the vehicle economy simulation model was built, and "City-Suburban-Highway-Suburban-City" comprehensive driving conditions were constructed taking the reduction of the equivalent fuel consumption as the optimization target. The PHEV dynamic parameters and controlling parameters of mode switching rules were optimized under the comprehensive driving cycle by using Genetic Algorithm (GA). The result demonstrates that, by using the method proposed in this paper, a set of reasonable power and control system parameters can be optimized to lower the vehicle equivalent fuel consumption, where the equivalent fuel consumption per 100 km can be reduced by 7.2% when compared with that of non-optimization cases.