A gain scheduling three-loop autopilot was set up to realize the real-time change flight trajectory of a missile,and its structure characteristics,feedback parameter acquiring,control performance and the transfer flight ability were researched.With the principle of state feedback and the pole assignment,a missile longitudinal flight control mathematical model was established,then the influence of the missile velocity,dynamic pressure and the elevator efficiency on the control instruction were analyzed in a typical three-loop autopilot.Combing with gain scheduling theory,the variables of velocity ratio,dynamic pressure ratio and elevator efficiency ratio were induced to correct the system nonlinearity,and the method to get feedback parameters was derived.In the end,three-loop robust stability was also analyzed.The comparison of the calculation results and the flight test data shows that the measuring accuracy of atmospheric density and atmospheric temperature is better than 1.7% and 3.0%,respectively,and the semi-physical simulation experiments prove that when the velocity changes to 20.6% in the variable trajectory,the cut-off frequency,overload steady-state gain and the phase margin are changed from 41.78 rad/s,0.87,78.19° to 41.71 rad/s,0.88 and 72.5°,respectively.Moreover,the phase margin is also larger 71.46° than the minimum of basic trajectory,and the autopilot still keeps a good control characteristic when the dynamic pressure changes 77.6%.These results prove that the gain scheduling three-loop autopilot meets the requirement of missiles for real-time transfer trajectory flight control.