In order to solve the problems of high cost, large volume and difficult maintenance when traditional mechanical sensors are used in permanent magnet synchronous motor, a sensorless system model of permanent magnet synchronous motor based on untracked Kalman observer is established in this paper, and the running state of permanent magnet synchronous motor is predicted by untracked Kalman algorithm to achieve closed-loop control. The simulation results show that the traceless Kalman observer has the advantages of accurate prediction, good dynamic and static performance, and strong anti-interference ability. It solves the defects of traditional permanent mechanical sensors to a large extent and has great application prospects in the future.