The paper aims at parameter matching problems of single-axle PHEV (parallel hybrid electric vehicle) in the early stage of the design, fuel economy as the design object, and presents the parameter selection criterion of the engine, motor and battery in the dynamic system. The scope of the enginepsilas power is determined by calculating the economic cruising power of the engine, the load characteristics chart and the universal characteristic chart are given by test, and based on that, the motor and battery parameters are selected, finally, the reasonableness of the selection criterion is checked by the simulation analysis. The reasonable selection of the system parameters provides the basis for the optimization of the vehicle control strategy.