A linear active disturbance rejection controller was designed for the trajectory tracking control system of a quad-rotor UAV to reduce the effects of parameter variations and external disturbances.The Linear Active Disturbance Rejection Controller (LADRC) can well overcome the problems of strong coupling,model uncertainty,and external disturbances.In this paper,the quad-rotor UAV trajectory tracking control system is divided into two loops:the outer loop uses a simple PD controller,and the inner loop uses a linear active disturbance rejection controller.The trajectory tracking experiment was performed on the linear active disturbance rejection control system on the simulation platform,and it was compared with the traditional PID control system.Simulation results show that the linear active disturbance rejection controller not only accurately estimates and compensates the internal/external disturbances,but also implements the quad-rotor flight control with robustness under the condition of dynamic parametric uncertainties.The controller meets the design requirements of fast attitude maneuver and high stability,and shows a superior performance to PID controller.