The development of electric motorcycle technology, the battery is a key motive force source. The traditional lead-acid battery has not accorded with the demand yet. The Lithium-ion battery has the high energy density and the high circulation performance, enhances the instantaneous horsepower output and the endurance. But the one that charged technology to the Lithium-ion battery is inappropriate, it is apt to cause the damage of the battery. So the design of the charger has very great influence on lifetime of the battery. For design of Lithium-ion battery characteristic demand, the flyback converter will offer the constant current and voltage definitely to charge. In order to prevent the Lithium-ion battery overcharging, this research is adopted feedback control to adjust duty cycle by pulse width modulation. The demand for constant current and voltage of the Lithium-ion battery charger will be realized.