This　study　proposes　an　improved　sensorless　control　method　for　sliding　mode　observers　to　solve　the　problems　of　high-frequency　chattering　and　poor　observation　accuracy　in　the　sensorless　control　systems　of　permanent　magnet　synchronous　motors.　The　hyperbolic　tangent　function　is　used　to　replace　the　traditional　switching　function.　The　estimation　algorithm　of　the　rotor　position　of　the　sliding　mode　observer　is　derived　from　the　hyperbolic　tangent　function.　The　Lyapunov　stability　analysis　method　is　used　to　analyze　the　stability　of　the　system,　and　sufficient　conditions　for　entering　the　sliding　mode　surface　are　obtained.　A　Kalman　filter　is　utilized　to　filter　the　back　electromotive　force,　and　a　phase-locked　loop　is　used　to　obtain　the　rotor　position.　Results　reflect　the　great　improvement　of　observation　accuracy　in　terms　of　speed　and　position.　The　simulation　model　of　the　improved　sliding　mode　observer　is　built　on　the　Simulink　platform,　and　the　results　are　compared　with　those　of　the　switching　and　saturation　functions.　Results　indicate　that　the　starting　process　of　the　improved　sliding　mode　observer　is　stable　and　that　the　high-frequency　chattering　in　the　steady-state　operation　process　is　obviously　weakened.　The　improved　sliding　mode　observer　achieves　high　observation　accuracy,　strong　anti-interference　ability,　and　stability.　Copyright　©2021　Journal　of　Harbin　Engineering　University.