A pitch plane switching-gain variable structure autopilot was designed for a missile controlled by aero tails to improve the performance of classical three-loop autopilot. The close-loop response is insensitive to parameter variation of missile body by applying switching-gain variable structure methodology. The control signal is smooth without high-frequency oscillation which is disadvantageous for actuators. The controllers for all flight envelopes can be easily achieved when gain-scheduling is used. The simulation result shows that the design method is valid.