The present invention discloses an on-board charging system for an electric vehicle, the system comprising: a three-phase power source connected in series in sequence, a first three-phase motor, a first three-phase inverter, a second three-phase inverter, a second three-phase motor, a battery pack, a first contactor, a second contactor, a third contactor, and a fourth contactor. The three-phase power source includes an upper road power source, a middle road power source, and a lower road power source, and the first three-phase motor includes an upper winding, a middle winding, and a lower winding. One end of the first contactor is connected to the upper winding, and the other end is used to be connected to the upper road power source or the middle winding. One end of the second contactor is connected to the middle winding, and the other end is used to be connected to the middle road power source or the lower winding. One end of the third contactor is connected to the lower road power source, and the other end is connected to the lower winding. One end of the fourth contactor is connected to the battery pack, and the other end is connected to the second three-phase motor or the second three-phase inverter. The present invention does not need to additionally increase an inductor to complete the charging operation, and has a simple structure, a smaller volume, and a lower production cost.