A trajectory tracking control scheme based on an improved nonlinear disturbance observer is presented to address the position and attitude errors caused by inaccurate modeling and vulnerability to external disturbances of wall-climbing robots. First, a kinematic controller is designed through back stepping control to provide reference centroid velocity and angular velocity for dynamic control of robots. Secondly, an improved nonlinear disturbance observer serves as a feed forward controller to estimate modeling errors and external disturbances of the dynamic model, ensuring exponential convergence of disturbance errors. Finally, a sliding mode controller is designed based on the dynamic model with an interference observer. The scheme compensates for external disturbances quickly and its stability is proven by Lyapunov’s theorem. The simulation results demonstrate that the control scheme performs well in avoiding modeling errors and external interferences.