A super-twisting control strategy based on improved sliding mode observer is proposed aiming at the problems of trajectory tracking control of quadrotor UAVs under uncertain disturbances.Firstly,a high-speed third-order sliding mode observer is proposed by improving the traditional sliding mode observer,which can estimate the system state and unknown disturbance more accurately and more quickly.Then,based on the proposed observer,and also on the basis of super-twisting theory and non-singular terminal sliding mode theory,a non-singular,super-twisting terminal sliding mode controller based on the high-speed third-order sliding mode observer is designed to realize tracking and controlling of the trajectory.The stability of the controller is proved by using the Lyapunov theory.Finally,the simulation results show that the proposed strategy has faster response speed and higher precision.