The main influencing factors of starting system under low temperature were analyzed, while maximum output power of the ISG motor was determined. According to starting resistance torque, minimum start-up speed, electrical operating characteristics, electric transmission coefficient and thermal effects, the influence of plate structure on battery capacity was also reviewed. The match relationship among starting resistance torque, ISG motor power and storage battery capacitance was summarized, and the changes of starting resistance torque along with ambient temperature and starting speed has been measured. The experiment result shows that as far as the environment temperature decreases by 5℃, starting resistance torque increases by 3~5N?m at above 200r/min; keeping speed constant, starting resistance torque increases by 4～11N?m with every enhanced 50r/min. The first fire speed of ISG diesel engine at -25℃ is increased, which is up to more than 350r/min .The starting time is shorter than original diesel engine, and fluctuations in speed is smaller.