The invention relates to a pressure-free plugging device, and mainly solves the problems that an existing plugging device needs a pump truck to press, the anchoring is not firm, and the sealing effectis poor. The device is characterized in that the upper part of a locking nut (1) is connected with a locking iron (9); the external part of the locking iron (9) is sequentially sleeved with a front plug sleeve (4) and a front rubber ring (5) from bottom to top; a spring (3) is arranged between the locking nut (1) and the front plug sleeve (4); the outer wall of the upper section of the locking iron (9) is in a cone shape, two axial sliding grooves are formed in the outer surface of the cone, sliding blocks (10) are connected with the sliding grooves, a plug (11) is connected with the upper end of the locking iron (9); a lock rod (2) is arranged in a cavity in the lower end of the lock iron (9); a steel ball (12) is embedded in the side wall of the lock iron (9); and a circumferential clamping groove (13) is formed in the outer wall of the lock rod (2). The pressure-free plugging device does not need a pump truck to press or a steel wire to plug, and has the advantages of high successrate of plugging, firm anchoring and a good sealing effect.