Abstract: Aiming at the problems of high-frequency chattering and rotor phase lag in the sensorless vector control of permanent magnet synchronous motors (PMSM) using traditional sliding mode observers, an improved sliding mode observer control method was proposed. First, a novel fast terminal sliding mode surface was constructed to accelerate the convergence of system state variables, which effectively suppressed system chattering while reducing the error of observed currents. Next, a control law with adaptive sliding mode gain was designed to address the system instability caused by variations in motor speed. Finally, a frequency complex coefficient filter was adopted to further filter the back electromotive force, and a quadrature phase-locked loop was utilized to accurately extract rotor position and speed information, thereby reducing phase lag.Simulation and experimental results demonstrate that, compared with the traditional sliding mode observer control method, the proposed method reduces the phase lag of the rotor position by approximately 0.290 rad and controls the speed estimation error within ±0.5 r/min when applied to the sensorless vector control of PMSM. The experimental results are found to be in strong agreement with the simulation results, which further verifies that the proposed method offers advantages such as reduced system chattering, strong anti-interference capability, and high estimation accuracy. This research is considered to provide not only an effective engineering solution to the inherent chattering and phase lag problems of traditional sliding mode observers, but also a reliable practical basis for promoting the application of high-performance sensorless drive technology for permanent magnet synchronous motors in industrial settings.