The invention provides a machine for automatically milling a gap of a piston ring. The machine comprises a panel (1) as well as a feeding assembly (2), a loading assembly (3), a pressing assembly (4) and a guiding and positioning assembly (5) which are arranged on the panel (1), wherein the loading assembly (3) is arranged between the feeding assembly (2) and the guiding and positioning assembly (5), and the pressing assembly (4) is arranged in the middle of the guiding and positioning assembly (5). The machine for automatically milling the gap of the piston ring is convenient to operate, the labor intensity is small, the production efficiency is greatly improved, and the product quality is guaranteed.