To solve many defects existing in the mechanical speed sensor of servo system, a fuzzy sliding mode speed observer was proposed for the feed system of the permanent magnet synchronous motor. Focused on the chattering problem of conventional sliding mode observer (SMO), sigmoid function was used instead of the traditional ideal switch function and fuzzy control system was used to adjust the gain of the SMO. This method could decrease undesirable chattering phenomenon and realized the soft control. Detecting back EMF could be done directly from switching signal without any low pass filter. So the delay time because of lowpass filter, in the proposed observer was eliminated and there was no need to compensate phase fault in position estimating. The asymptotic stability of the designed sliding mode observer was proved by Lyapunov function. The simulation results showed that the designed fuzzy sliding mode observer could accurately identify the rotor speed of PMSM, and had good dynamic and static performance.