A practical configuration of the power train for the parallel hybrid electric vehicle (HEV) is presented in this paper. The parameters of the power unit (included engine, motor, battery) that must be considered and determined during parallel HEV designing are calculated and discussed in details according to the vehicle requirements for maximum speed, acceleration time, maximum grade ability, emission, fuel efficiency. The parameters of the battery are determined by calculation and the measures that will be taken in design are also discussed in this paper. In cycles it must be insured that the consumed energy and absorbed energy through regenerative braking are balance. Thus the battery pack will never have to recharge from wall plug, the range is as long as conventional vehicle. The ratio of torque-combination device, transmission and the final drive gear is optimized and determined respectively based on the vehicle criteria of traction performance and the fuel economy.