In order to realize the position sensorless control of permanent magnet synchronous motor （PMSM） with wide speed range, a wide speed position sensorless control strategy based on the improved sliding mode method is proposed. In the medium and highspeed stage of the motor, a new sliding mode reaching law is designed to suppress the inherent chattering problem of the traditional sliding mode observer. Thus, the estimation accuracy of the motor speed is improved. In the zero and low speed stage of the motor, the pulsating high frequency injection method is used to estimate the speed of motor. In addition, a smooth switching control strategy is designed to achieve smooth switching between different algorithms. The comparison of simulation results verifies that the designed controller has good speed estimation and tracking performance, and the smooth switching of different control algorithms can be achieved.