Abrupt stator fault when the frequency converter sets under steady running state is one of ordinary faults of frequency converter sets which will bring big economic loss and bad society effort. Usually, wavelet transform module maximum accords with saltation points. Distortion in stator current will be caused by abrupt stator fault when the frequency converter sets under steady running state. Usually, wavelet transform module maximum accord with saltation points. Inner fault and external fault module of frequency converter sets stator are established by Matlab/Simulink.The two modules are detected by Wavelet transform module maximum method , which not only can detect stator fault but also can time it, which realize the diagnosis of frequency converter sets.