Considering the problems of nonlinearity,uncertainty,and coupling existed in system model of longitudinal control system of short-range loitering missile,Active Disturbance Rejection Controller (ADRC) is integrated to deal with them.The structure,principle,algorithm implementation and parameter setting rules of ADRC are presented here.As to the trembling phenomenon and control performance degradation when the linear interval width of Extended State Observer (ESO)is small,a method of improved nonlinear function is proposed for design of the longitudinal motion control system.The result of simulation experiments with Simulink platform show that:1) The improved method effectively solves the problem of trembling and enhances the controller performance;and 2) The control system based on improved ADRC has good control performance.Therefore,the rationality of the improved method and control system is verified.