The power converter applied to switched reluctance motor (SRM) drive system was a key link to the system reliability. Abnormal operation with faults for a long time could cause the collapse of the whole system, which indicated that the fault diagnosis for power converter in SRM had a large significance. The discrete wavelet transform method was used to extract the ratio of phase current mean to standard deviation which could be taken as the diagnostic feature. Four types of faults of power converter were analyzed and discussed. Determination of fault types and fault devices was implemented. Finally, the feasibility and effectiveness of the proposed method were proved by simulation and experiment.