Aimed at the four typical electrical troubles of power converter in the switched reluctance starting/generation system，and on the basis of analyzing upper and lower following current，and introduction of digitizer ，a new method of fault diagnosis is proposed. Converter's operational principle and the energy convent process are analyzed. The effects of faults on the upper and lower following current are analyzed in exciting state and currentfollowing state, then, according to the faultfeature, the scheme of fault diagnosis is put forward based on the difference between upper and lower following current. Finally, a fault diagnose model of switched reluctance starter/generator is built and validated. The result shows that the fault diagnosis scheme is more accurate than that of the fault diagnosis with only phasecurrent.