In order to suppress the interference from internal and external complex space environments for spacecraft, and to further improve the attitude controlling accuracy and stability of satellite, a back-stepping sliding mode controller based on nonlinear disturbance observer was designed. Firstly, a sliding mode controller was designed using back-stepping theory, and the stability analysis process was provided. This resulted in a significant reduction in attitude adjustment time while balancing the steady-state and dynamic performance of the system. Secondly, a nonlinear disturbance observer was designed to observe the interference caused by environmental torque, parameter uncertainty, etc., and the asymptotic convergence of disturbance observation error was analyzed. Finally, the effectiveness of the algorithm was confirmed through mathematical simulation.