Abstract: In view of problems of low power quality, low cruising power, short service life of battery, separation between battery charging device and locomotive driving system existed in current charging system of mine-used electric locomotive with lead-acid battery, a new integrated on-board charging system was designed. The system is composed of the front-stage PWM rectifier circuit and the back-stage Buck circuit in series. When charging, the motor windings are reconstructed into the boost inductance of the PWM rectifier circuit to form an integrated on-board charging and discharging circuit. The supercapacitor is used to replace the battery as the energy storage element, which can realize quick on-board charging and discharging function. The simulation results show the system has shorter charging time and higher efficiency, and can realize functions such as power factor correction, ripple suppression, efficient and rapid charging and discharging compared with the traditional charging system.