The invention discloses a method for diagnosing wavelet transformation ratio faults of power converters of switch reluctance motors, and belongs to the technical field of diagnosis of faults of motordriving systems. The method for diagnosing faults of main switch tubes of the power converters of wavelet transformation switch reluctance motor systems includes acquiring normal and fault phase currents from the power converters of the switch reluctance motor systems; carrying out three-layer wavelet transformation on the phase currents by selected db3 wavelets to obtain third-layer low-frequencycoefficients and computing average values and standard deviation of the third-layer low-frequency coefficients; utilizing ratios mu of the obtained average values to the obtained standard deviation as fault diagnosis characteristic values and diagnosing power short-circuit and open-circuit faults. The method has the advantages that db3 wavelet analysis is carried out on the phase currents under normal and fault conditions, the ratios of the average values to the standard deviation of three-layer wavelet transformation low-frequency coefficients obtained by means of analysis are used as the characteristic values, and accordingly the faults can be effectively diagnosed by the aid of the method; the faults can be accurately diagnosed by the aid of the diagnosis characteristic values under rotational speed and torque change conditions, accordingly, certain robustness can be embodied, and the method has certain engineering application value.