Abstract: Y221 packer is extensively used in packer string, but when conventional Y221 packer is set, the tubing and pump cylinder above the packer shall bend and deform axially under the action of weight, which exacerbates eccentric wear on tubing and rod and increases the load on pumping unit. In view of this problem, a self-locking Y221 packer has been developed. This paper sets forth the working principle of this packer and verifies the anchoring force of the packer slips in line with the proper weight of packer rubber tube and calculates the unlocking load. In addition, a setting tool for this self-locking Y221 packer has been designed, which ensures that the packer is not unlocked while the tubing hanger can successfully sit in the wellhead when the weight is removed, so the string is tied back in hole. A self-locking mechanism and duel-stage unlocking mechanism are added inside the packer, so after the packer is set and the weight is released, the packer can still stay set while the string above the packer is in a free state, hence reducing the up and down friction of the sucker rod and the load on pumping unit. However, this string has some limitation in its self-locking performance, that is, the packer can be set many times, but it can realize self-locking after it is first set and cannot self-lock after being set twice.