The invention relates to a locking method of a one-way valve of a positive displacement piston diaphragm pump, which can be used for conveniently mounting a locking nut onto a valve cone. The locking method adopts the technical scheme that the inner wall of a valve seat is uniformly provided with 3-4 bosses; the valve cone of the one-way valve of the positive displacement piston diaphragm pump is arranged in the valve seat, and after a valve ring is put in, the locking nut is put on the valve ring; and the bosses are utilized to limit three brackets of the valve cone so as to screw down the locking nut.