An auto compression valve, comprising a rear housing with an air release hole; a front housing screwed with the rear housing; a taper piston moveably mounted in the rear housing; a spring mounted in the front housing, wherein one end of the spring is placed in the cavity of the front housing, another end is sleeved on the cylinder end of the taper piton; a lock ring with an air release groove fixed between the rear and front housings. Air release is realized through the air release hole and the air release groove, thus all parts of the valve can be assembled more tightly to prevent coming loose, maintaining the necessary pressure for inflating tires and controlling the air leaking flow in deflation.