Abstract: To design the three-loop autopilot properly,the characteristics and operation principle have been analyzed.It has been concluded that the inner loop of a three-loop autopilot is an attitude autopilot,it can make an unstable missile stable;missile aerodynamic coefficient change and fin control surface bias do not have effects on the steady state outputs of three-loop autopilots.Also,compared with an integration compensated acceleration autopilot,faster response can be obtained with a three-loop(autopilot.) A three-loop autopilot also has a better filtering response for noisy input.