The invention provides a packer which comprises a central tube as well as a locking mechanism, an actuating mechanism, a sealing mechanism and an anchor mechanism which are arranged outside the central tube, wherein the actuating mechanism enables the sealing mechanism and the anchor mechanism to act; the locking mechanism comprises a lock sleeve adjacent to the sealing mechanism, a locating component arranged outside the lock sleeve, a right-hand nut and a left-hand nut arranged inside the lock sleeve and spaced at an interval, and a right-hand thread section and a left-hand thread section arranged on the outer wall of the central tube and corresponding to the right-hand nut and the left-hand nut; a through hole is arranged on the wall, corresponding to the lock sleeve, of the central tube and a baffle is arranged outside the wall of the tube; the baffle and the inner wall surface of the lock sleeve are sealed and connected to form a cylinder bottom of a piston cavity; and the actuating mechanism comprises a piston arranged in the piston cavity and connected with the lock sleeve and an unpacking elastic component connected with the piston. The packer has the advantages that the prevention of midway setting and setting failure can be effectively realized, the working reliability is improved, the multi-time setting and unpacking in one string can be realized, the borehole operation procedure is simplified, the working efficiency is improved, and the cost is greatly saved.