In the speed control system of permanent magnet synchronous motor (PMSM), it is proposed to adopt the active disturbance rejection control (ADRC) to design the speed loop. According to the control performance of the speed control system and the characteristics of the ADRC strategy, the extended state observer in the ADRC is improved. At the same time, the nonlinear extended state observer (NESO) is used for both the observation of the system load torque and the feedforward compensation, so as to reduce the influence of load torque disturbance. Based on the above two measures, an improved ADRC (IADRC) controller of speed loop is designed. The effectiveness of the IADRC controller in the speed control system of PMSM is verified by simulation and experiments.