In view of the relationship between each Degree of Freedom (DOF) of the 3DOF helicopter system,the helicopter system is divided into an actuated subsystem and a non-actuated subsystem.The mathematical model of the 3DOF helicopter is established,which depicts the possible external disturbances and sensor failures of the non-actuated subsystem.A nonlinear extended disturbance observer is designed to eliminate the adverse effects caused by external disturbances and sensor failures,and a high-order sliding mode controller is designed to realize tracking control of the actuated subsystem.The stability of the system is proved by Lyapunov theory.Finally,the experimental results illustrate that the control scheme has good effects on the 3DOF helicopter with sensor failures.