The invention relates to the technical field of hardware wrenches, in particular to a sleeve for quickly mounting and dismounting a circular nut. The sleeve comprises a threaded elastic sleeve capable of sleeving the circular nut required to be mounted and dismounted; a circular truncated cone body expanding from top to bottom is arranged at the lower part of the threaded elastic sleeve; axial through grooves distributed circumferentially and evenly are formed in the outer circumferential surface of the circular truncated cone body; a hollow cylinder bulging upwards is arranged in the middle of the circular truncated cone body; an external thread is arranged on the outer wall surface of the hollow cylinder; the middle of the upper end surface of the cylinder is an outer hexagonal structure body; a square hole matched with a torque wrench for use is formed in the center of the outer hexagonal structure body; the sleeve further comprises a threaded locking sleeve capable of sleeving the outer side of the threaded elastic sleeve; the lower part of the threaded locking sleeve is matched with the circular truncated cone body at the lower part of the threaded elastic sleeve; and the upper part of the threaded locking sleeve is in threaded connection with the threaded elastic sleeve. With the sleeve, the problems of low pre-tightening precision, high dismounting working intensity and low efficiency of the circular nut are effectively solved.