In order to meet the high-precision requirements of a new fixed-aiming servo control system, the servo controller of the servo system is redesigned.The composition and working principle of the fixed-aiming servo system are introduced, and the mathematical model of each module of the system is established. The Auto-Disturbance Rejection Controller (ADRC) is applied to the system's speed loop, and the improved Nonlinear PID (NLPID) controller is applied to the current loop.The system is simulated by the S-Function module in the Matlab/Simulink simulation environment. The simulation results show that, the designed controller not only has high tracking accuracy, but also has good disturbance isolation performance, high adaptability and strong robustness, which provides a theoretical reference for the further study of high-precision fixed-aiming servo system.