A sliding mode adaptive iterative learning control algorithm is proposed for trajectory tracking of a quadrotor UAV under external disturbances.The designed controller consists of two parts.The first part is the sliding mode sub-controller,which is taken as the feedback controller of the quadrotor UAV system.The second part is the iterative learning sub-controller,which is taken as the feedforward controller of the quadrotor UAV system.In the iterative learning process,the control gain of the iterative learning sub-controller can be adaptively changed according to the trajectory tracking error,and this can improve the trajectory tracking performance of the quadrotor UAV.Finally,the effectiveness of the algorithm for the trajectory tracking of a quadrotor UAV is verified by software simulation.