In order to improve the system′s robustness to unknown disturbances and parameter changes, the active disturbance rejection control (ADRC) strategy is introduced into the permanent magnet synchronous motor (PMSM) position servo system, and the ADRC strategy is improved to make the system meet the requirements of high servo control performance. By improving the structure of the extended state observer (ESO) in ADRC, the observation speed of observer is increased. At the same time, in view of the error between the actual moment of inertia and the inertia used in ADRC, which affects the selection of the control gain in the speed ADRC controller, an online inertia identification method is adopted to adjust the controller parameter in real time. Based on the above two improvement measures, the improved ADRC controllers for the speed and position loops are designed, fundamentally improving the dynamic performance and antidisturbance capability of the system. Finally, the effectiveness of the improved ADRC strategy in the PMSM position servo system is verified by simulation.