The traditional PI controller has some problems in permanent magnet synchronous motor (PMSM) servo control, such as overspeed and poor resistance to external disturbance. To solve the above problems, a linear extended state estimator (LESO) was designed to improve the observation accuracy of the active disturbance rejection controller for internal and external disturbances. A linear active disturbance rejection (LADRC) system based on the improved LESO was designed for the PMSM servo speed control system. Through simulation and experiment, it was verified that the PMSM servo system based on the improved LADRC can achieve higher observation accuracy, fast and high precision control of speed without overshoot, and good robustness to load disturbance.