The invention relates to a planetary reduction stepless variable speed coupling box of a new energy automobile. The planetary reduction stepless variable speed coupling box comprises a main drive loop formed by motors, planetary reduction mechanisms and a differential mechanism, wherein the motors are connected with sun wheels of the planetary reduction mechanisms through rotor frames to be used as power input, and planet carriers of the planetary reduction mechanisms are connected with the differential mechanism to be used as power output drive wheels. The planetary reduction stepless variable speed coupling box of the new energy automobile further comprises an auxiliary drive device for driving inner gear rings of the planetary reduction mechanisms to rotate. Compared with the prior art, the main drive loop can carry out gear switching of different speed ratios on a planet gearbox according to the working conditions of the inner gear rings, and therefore the whole gear shifting process is continuous, stable and free of impact force, so that stepless variable speed of the automobile in climbing, heavy-load starting, common-load driving at the moderate speed and light-load driving at high speed can be achieved.