In allusion to the defects of traditional theory matching method, the authors propose a new power matching method which combines theoretic calculation and cycle working condition together for powertrain of pure electric automobiles. Based on dynamic constraint, the peak power of motor is determined. In order to make the motor work in high efficiency area, the power needed by vehicles in ten cycles is analyzed and the motor rated power is determined. Regular effect pattern of battery parameters on dynamic property and driving range of entire vehicle is analyzed. With defining a conception of acceleration time influence factor and continue driving range influence factor, motor parameters are amended. The transmission ratio is optimized with taking the power of the entire vehicle as constraint and the maximum driving range in constant speed condition as object, and the driving range is greatly improved. The output power of battery in different SOCs is simulated, and it’s found that when the SOC closes to lower limit, the output power of battery is able to satisfy the demand of the vehicle.