Abstract: In view of problems of big torque fluctuation and easy to be influenced by load change existed in direct torque control system of permanent magnet synchronous motor based on PI controller, the paper designed an active disturbance rejection controller based on speed loop to replace PI controller to improve performances of direct torque control system of permanent magnet synchronous motor. It used particle swarm optimizer algorithm to make optimization calculation for the parameters of the active disturbance rejection controller and improved adjustment performance of the controller. The simulation and experimental results show that the system based on the active disturbance rejection controller with parameters optimization has higher ability of anti-disturbance of load, faster response speed and good dynamic and static performance.