Aiming at the problems of model nonlinear, strong coupling, as well as external disturbance of submarine in the depth control process, a sliding backstepping control strategy is proposed based on the nonlinear disturbance observer(NDO). The NDO is used to observe the uncertainties and disturbance of the system. The disturbance observer errors is in exponential convergence by electing disturbance observer. Aiming at the characteristics of dual channel coupling of the submarine vertical plane control system, the bow and stem rudder controller is used to control the depth and the pitch respectively. By using the sliding backstepping controller, the closed loop system global asymptotic stability is proved based on the Lyapunov stability theorem. Simulation results show the effectiveness of the proposed approach.