Aiming at the problem that the change of motor parameters in actual operation will significantly reduce the control accuracy of the motor, this paper proposes a sensorless control method of permanent magnet synchronous motor based on an adaptive back-EMF observer. In the sensorless vector control algorithm, the mathematical model of the permanent magnet synchronous motor based on the coordinate axis transformation is established, the flux linkage of the permanent magnet synchronous motor is identified online, and the motor model is updated with the specified parameters, to realize the analysis of the rotor position and the permanent magnet synchronous motor. Accurate control of rotational speed. The back-EMF observer and the adaptive back-EMF observer are verified in the simulation environment. The simulation results show that the adaptive back-EMF observer can quickly converge to the actual value and track the motor parameters well. Enabling highly accurate rotor speed and position estimation. Finally, the permanent magnet synchronous motor control platform is built in the laboratory. Under the condition of the parameter change of the permanent magnet synchronous motor, the online identification of the parameters and the accurate control of the speed of the permanent magnet synchronous motor can be realized.