A new NC copying machining technique for non-circular piston ring is introduced, which makes it possible to work piston rings with different pressure distribution curve using a kind of cam, and realize error compensation while cam or cutting tool wears away. It improves the flexiblility and precision of machine. Moreover, the problem of disturbance resistance is resolved by an intelligent method of making policy combine with fuzzy control technology. It improves the system robustness, as well.