The invention discloses an unloading device used for a driven end of belt transmission of a high-power and high-rotation-speed motor. The unloading device comprises an unloading support, an unloading bearing seat, an unloading unit and an unloading shaft. The unloading bearing seat 4 is fixedly installed on the unloading support. The unloading unit comprises an angular contact ball bearing set, a spacer bush, two bearing glands and a locking nut. The angular contact ball bearing set comprises two angular contact ball bearings which are oppositely assembled in the unloading bearing seat and used for supporting rotation of the unloading shaft. The bearing glands are connected and fastened to the unloading bearing seat through bolts, and the axial position of the angular contact ball bearings is fixed through the cooperation of the bearing glands and a shaft shoulder of the unloading shaft. The spacer bush is arranged in an inner hole of the unloading bearing seat, outer rings of the two angular contact ball bearings are spaced, and thus the axial position of the angular contact ball bearings can be fixed. By the adoption of the unloading device, the radial force generated by belt transmission to a driven shaft can be eliminated, the vibration transferred to the driven shaft is reduced, and the operation precision and operation stability of the driven shaft are improved.