In order to meet the anti-disturbance performance of the Self-Propelled Anti-Aircraft Gun (SPAAG) turret pitch servo system, the servo controller of the system was redesigned. The composition and working principle of the servo system were studied, and the mathematical model of each module of the system was established. The model compensation Active Disturbance Rejection Control (ADRC) for pitch servo system was proposed. By using the Recursive Least Squares (RLS) method of variable forgetting factor, and by inputting the cross-axis current and the actual rotational speed, the resistance torque and impact load of the servo system were obtained, which were used for compensation of the ADRC. The system was simulated by the S-Function module in the Matlab/Simulink simulation environment. The simulation results show that this algorithm can generally increase the ability of extended state observer for estimating disturbance, and can enhance the robustness and control precision of systems.