Abstract Aiming at the nonlinear links in the mechanical transmission structure design of the servo system of a large planar mirror turntable and the characteristic that parameters are difficult to identify, this paper designs an active disturbance rejection controller based on an improved nonlinear function to achieve the position servo control of the turntable. Firstly, the physical model of the turntable is built by using the MATLAB/Simulink Simscape-Multibody toolbox, and the mathematical model of the rotating motor is simplified to obtain the overall simulation model of the controlled object. Secondly, a second-order active disturbance rejection controller is designed. On this basis, a scheme for improving the nonlinear function is proposed and its convergence is proved. Finally, simulation experiments are completed on the MATLAB/Simulink platform. The experimental results show that the improved ADRC controller has higher tracking accuracy, faster dynamic response speed, and better anti-interference ability.