This paper presents a novel control method by integrating the sliding mode disturbance observerbased control and the backstepping control technique,and successfully applies it to a flight control system for heavy cargo airdrop operations.The super-twisting second order sliding mode disturbance observer(SOSMDO)is employed to estimate bounded but otherwise arbitrary disturbances,thus ensuring asymptotic convergence of the estimation error to zero in a finite time.Besides,the integrated controller can significantly improve the robustness of the flight control system to modeling uncertainty and external disturbance in the presence of state/control constraints.The closed-loop stability is guaranteed in the sense of Lyapunov.In addition,the proposed approach can considerably reduce design cycles.The performance of the proposed control method is demonstrated in a very low altitude extraction airdrop simulation with a high-fidelity six-degree-of-freedom transport aircraft model. This paper presents a novel control method by integrating the sliding mode disturbance observerbased control and the backstepping control technique, and successfully applied it to a flight control system for heavy cargo airdrop operations. Super-twisting second order sliding mode disturbance observer (SOSMDO) is employed to estimate bounded but otherwise arbitrary disturbances, thus ensuring asymptotic convergence of the estimation error to zero in a finite time.Besides, the integrated controller can significantly improve the robustness of the flight control system to modeling uncertainty and external disturbance in the presence of state / control constraints.The closed-loop stability is guaranteed in the sense of Lyapunov. addition, the proposed approach can substantially reduce design cycles. The performance of the proposed control method is demonstrated in a very low altitude extraction airdrop simulation with a high- fidelity six-degree-of-freedom transport aircraft model.