An　improved　active　disturbance　rejection　control　(I-ADRC)　to　improve　the　disturbance　attenuation　of　a　permanent　magnet　synchronous　motor　speed　controller　was　proposed　in　this　paper.　A　nonlinear　function　with　improved　smoothness　was　adopted　to　design　the　controller.　The　Lyapunov　stability　of　the　improved　tracking　differentiator,　the　improved　extended　state　observer,　and　the　controller　were　analysed.　Moreover,　simulations　and　experiments　confirmed　the　effectiveness　of　the　proposed　controller.　The　results　demonstrate　that　the　proposed　controller　has　a　smaller　steady-state　error　and　a　stronger　disturbance　attenuation　ability　than　the　proportional　integral　derivative　(PID)　controller.