Abstract: A cascade observer-based robust fault tolerant control method is proposed for the nonlinear non-minimum phase vertical take-off and landing (VTOL) aircraft model,with a guarantee that the system outputs asymptotically track desired trajectory. To begin with,two reduced-order cascade observers are designed to estimate unknown fault and disturbance information,respectively. Using the coordinate transformation and feedback linearization,the original system is decoupled into two tracking subsystems. Subsequently,a robust optimal control law and an optimal integral sliding mode control law are designed,respectively,based on the disturbance and fault estimate information in order to stabilize the two subsystems. Finally,the simulation results show the effectiveness and superiority of the proposed method.