In this paper, the author in-depth study on the key techniques of the AC servo system for manipulator. Through the analysis of the application characteristics of the manipulator servo control system, the joint position servo control algorithm is optimized to improve the position control accuracy of the joint output end. Permanent Magnet Synchronous Motor (PMSM) is selected as the servo drive system of the mechanical arm. Linear Auto-Disturbance Rejection(LADRC) control algorithm is designed to improve the speed loop and position loop of the control system, and the extended state observer is improved to improve the disturbance observation performance. At the same time, the inertia identification model of the system is designed with reference to the adaptive algorithm to reduce the influence of system inertia error on performance. The experimental results show that this method improves the disturbance performance and response speed of the system, thereby improving the position control precision of the joint[1].