A sliding mode control method is proposed to track the trajectory of a tilted quadrotor UAV in the rotor mode and the flight mode after the change of the nacelle angle.Firstly,the dynamic system of the tilted quadrotor UAV is considered as the combination of a fully-actuated subsystem and an underactuated subsystem.Secondly,by using the Extended State Observer (ESO),the control laws of the two subsystems are designed respectively.For the underactuated subsystem,the composite sliding surface is introduced,and the Hurwitz stability is used to solve the sliding surface coefficients.Then,based on Lyapunov stability theory,all subsystems can reach the sliding surface.Finally,the effectiveness of the proposed method is verified by comparative simulation experiments.