The invention provides an automatic demagnetization machine of a piston ring and relates to the field of processing of the piston ring. The automatic demagnetization machine comprises a rack, a feeding device, a conveyer belt, a demagnetization machine and a ring collator, wherein the feeding device comprises a bottom plate; the bottom plate is connected with a support seat and a first screw nut assembly; the bottom plate is provided with a V-shaped block connection plate, a V-shaped backup plate and a guide plate; the lower end of the V-shaped block connection plate is hinged in the support seat; the V-shaped backup plate is connected to the V-shaped block connection plate; elongated slots are formed in the V-shaped backup plate and the V-shaped block connection plate; a back-up ring frame is arranged between the V-shaped backup plate and the guide plate; a nut of the first screw nut assembly is connected with a feeding sliding block; the feeding sliding block is connected with the back-up ring frame; a guide rod is integrally arranged on the back-up ring frame and is arranged in the elongated slots; a conveyer belt bracket at a feeding end of the conveyer belt is connected with an air cylinder seat; the lower part of the air cylinder seat is connected with a transverse air cylinder; a telescopic end of the transverse air cylinder is connected with a vertical air cylinder; and the telescopic end of the vertical air cylinder is connected with a push plate. By the automatic demagnetization machine, the labor intensity of a worker is reduced; and the production efficiency is improved.