Compared with the aircraft which used wire flight control system, the aircraft that had mechanical control system was not provided with the flight envelope protection function, so the pilot may made the aircraft in stall with incorrect operation, especially in the trial test and the stall flight test when designing a new type of aircraft.Stall auto-protecting device can control reverse driving actuator to push the mechanical control system, restrain the pilot from leading the aircraft into stall, and eventually help the pilot to make the aircraft recover from stall. Fuzzy control theory has much more superiority than the conventional control theory, which can simplify the control law in a more efficient and direct way.