For the class of high-order nonlinear systems with unmatched disturbances and modeling error, an Adaptive Backstepping Non-singular Terminal Sliding Mode Control (ABNTSMC) scheme based on Nonlinear Disturbance Observer (NDO) is proposed combined with filtered backstepping method.Firstly, a finite-time stable nonlinear disturbance observer is designed to estimate and compensate for the unmatched disturbances.The backstepping method is employed to deal with high-order uncertain nonlinear systems.To avoid the explosion of differentiation in traditional backstepping control, the dynamic surface control method is used to design the virtual controller.In the nth step, a non-singular terminal sliding mode controller is designed based on the adaptive control and NDO to eliminate the effects of unmatched disturbances and modeling error on the systems.It is proved that the tracking error is guaranteed to be uniformly and ultimately bounded by using Lyapunov theorem.Finally, the simulation results prove the efficacy of the proposed method.