In order to reduce the impact of current noises to sliding mode observer and the requirements of sliding mode observer control algorithm to hardware, proposes a new sliding mode observer with pre-filter and post-filter and derives the stable condition of sliding mode control system by Lyapunov stability theory. The simulation experiments indicate that the sliding mode observer real-time tracks the rotor angle information accurately, and the control system has strong robustness and operates stably and reliably. Keywords ：sliding mode observer；pre-filter；post-filter；Lyapunov stability theory