In order to optimize the problems of high-frequency chattering, long response time, and large estimation errors of traditional sliding mode observers (SMO), this paper proposes an improved SMO. The sign function in the traditional SMO is replaced with a new piecewise exponential function to reduce the high-frequency chattering of the system, the arctangent algorithm with large errors is discarded, and the phase-locked loop is used to estimate the IPMSM speed and rotor position information. The Lyapunov stability criterion was used to prove the stability of the improved SMO, and the improved SMO sensorless control strategy model based on the interior permanent magnet synchronous motor was built through Matlab / Simulink, and simulation analysis was performed. The simulation results show that compared with the traditional SMO, the rotor position estimation error of the improved SMO is optimized from 0. 05 to 0. 025 rad, the system speed estimation response time is reduced by 50%, and the speed estimation error is reduced by 85%. It is proved that the improved SMO has higher dynamic performance and estimation accuracy.