The invention discloses a high-power energy-saving speed regulating system and method of a differential planet gear in parallel connection with a four-quadrant motor. The system comprises the differential planet gear, the four-quadrant motor, a four-quadrant inverter, a driving motor and a load; the differential planet gear comprises a drive bevel gear, a differential inner bevel gear set, a driven bevel gear and a differential outer gear; the differential inner bevel gear set comprises multiple inner bevel gears, and each inner bevel gear is arranged on the inner circumference of the differential outer gear; each inner bevel gear is meshed with the drive bevel gear and the driven bevel gear; the drive bevel gear is connected with the driving motor, and the driven bevel gear is connected with the load; the differential outer bevel gear is meshed with a motor gear in the four-quadrant motor; one end of the four-quadrant inverter is connected with the four-quadrant motor, a power networkis connected with the other end of the four-quadrant inverter, and the power network is further connected with the driving motor. The high-power energy-saving speed regulating system and method of the differential planet gear in parallel connection with the four-quadrant motor have no slip loss and can achieve speed increasing, reducing and regulating, rapid braking of the load and standby functions under the fault state of the driving motor.