The invention provides an automatic resetting device which is mounted between a rotor and a fixed frame and comprises a hinge fixed to the top of the fixed frame, a limiter transversely arranged at the top of the rotor and a sleeve assembly longitudinally arranged in the rotor. A connecting shaft is longitudinally arranged on the lower surface of the hinge and is provided with a longitudinally connecting hole; the transversely right end of the limiter is provided with a through hole; the sleeve assembly comprises a steel pipe and spring steel inserted inside the steel pipe, the steel pipe is mounted in the through hole, the top end of the spring steel is mounted in the connecting hole in a turnable way, and the bottom end of the spring steel is fixed to the steel pipe. The automatic resetting device is simple in structure, low in cost and capable of stably regulating the torsion, enables the rotor to apply a certain pressure to the fixed frame after the rotor is reset, and accordingly guarantees the sealing effect.