The invention discloses a polishing device for a hollow cup motor rotor. The polishing device has the technical advantages of simple structure, convenience in maintenance and high operation efficiency. The structure of the polishing device comprises an automatic feeding device and an automatic polishing device, wherein the automatic feeding device comprises a rail slot, a conveyer belt, a material level positioning device and a material stirring device; the material stirring device comprises a material stirring plate and a material plate driving device; the material stirring plate is equipped with a plurality of stirring forks; the material plate driving device is used for driving the material stirring plate to traverse on a plane as high as the plane of the rail slot; the automatic polishing device comprises a material rotation driving device, a polishing belt feeding device and a polishing executing device for driving the polishing belt feeding device to advance and retreat; the polishing belt feeding device comprises a base plate and a polishing belt; the base plate is equipped with a station slot; the polishing belt is arranged above the station slot. The polishing device provided by the invention can automatically polish the hollow cup motor rotor located in an automatic production line of the hollow cup motor rotor.