The invention discloses an automatic gap grinding machine for piston rings. The automatic gap grinding machine is composed of gap grinding machine adjusting stands, a machine body, a bedplate, a machine tool electric control device, a horizontal feeding device, a pushing device, a grinding head device, a gap grinding mold and a receiving device. The bedplate and the machine tool electric control device are fixed on the machine body. Automatic operation of the gap grinding machine from feeding, pushing, pressing and head grinding to receiving is realized. According to the technical scheme, the piston rings with the gaps opening upwards are subjected to feeding in a horizontal-hanging type numerical-control pushing mode, manual arranging and centering are omitted, precise positioning can be achieved during pushing, stability and reliability are achieved during pressing, production efficiency is improved, cost is lowered, and machining precision and machining quality of the pistons are guaranteed.