Demagnetization fault of permanent magnet synchronous motor was one of the most serious fault in motor fault. Demagnetization fault meant that the advantages of permanent magnet synchronous motor was significantly decreased. Put forward a diagnosis method based on CWTHHT of demagnetization fault for permanent magnet synchronous motor and analyzing its feasibility. Firstly, the steady state operation characteristics of permanent magnet synchronous motor were briefly analyzed, experimental platform of motor fault set up, stator current signal of normal and demagnetization of motor collected in real time; Then, the comparison and the analysis showed that the periodicity of component imf4 of current signal EMD decomposition under the demagnetization fault was worse and component imf3 accounted for a large proportion compared with the normal condition. The energy of the fundamental frequency band of current signal of the demagnetization fault was scattered. Therefore, the fault diagnosis method based on CWTHHT was feasible.