The invention discloses a breather valve, which comprises an expiratory and inspiratory device and a liquid leakage resistant device which is arranged under the expiratory and inspiratory device, wherein the liquid leakage resistant device comprises a lower valve body provided with a first channel; a cover plate of which the surface wall is provided with a plurality of holes is processed on the inner surface at the upper end of the lower valve body; a detachable lower valve cover is arranged on the inner surface at the lower end of the lower valve body; the lower valve cover is provided with a second channel; the side wall of the lower valve cover is provided with a through hole; a movable sealing component is positioned inside the second channel; a valve core of which the outer surface is provided with a convex shoulder and the inside is provided with a third channel is overlaid on the upper end face of the lower valve cover; the upper end of the valve core is sleeved on the inner surface of the cover plate; a first elastic component is positioned inside the first channel; and one end of the first elastic component leans against the upper end face of the convex shoulder, and the other end of the first elastic component leans against the lower end face of the cover plate. The breather valve can prevent a liquid from flowing out of a storage tank after the storage tank is turned over, and can also drive the liquid to flow out of the storage tank when the internal pressure of the storage tank reaches a predetermined value so as to prevent safety misadventures such as explosion of the storage tank.