The traditional winding open-circuit fault diagnosis methods of permanent magnet synchronous motor (PMSM) have low efficiency and poor adaptability. An adaptive threshold PMSM winding open-circuit fault diagnosis method based on the improved average current method is proposed. Firstly, the current signals of the PMSM three-phase normal state and fault state are obtained. Secondly, to overcome the influence of measurement noise, the signal is filtered by a sliding window. Thirdly, an improved average current method for winding open-circuit fault diagnosis is proposed. The improved average current method can obtain the adaptive threshold, and the comparison result between the filtered current value and the threshold is used as the basis for fault judgment. Finally, the proposed algorithm is verified by the simulation platform. The results show that the proposed method has advantage of quickness and strong stability.