Abstract: Induction motor variable frequency drive system has already been used in a wide variety of industry applications. It is very significant to carry out fault diagnosis of broken rotor bar in induction motor powered by a converter in variable frequency drive system. Up to now, the most published fault diagnosis approaches of broken rotor bar are usually based stator current signal spectrum analysis. However, the convenient acquisition signal is the secondary current of cubicle switchboard, namely power supply current （converter input current） in induction motor variable frequency drive system. This paper analyzes thoroughly the impact to power supply current caused by broken rotor bar fault, and then, completed spectrum analysis for power supply current and stator current （converter output current） signal. Simulation and experimental instances demonstrate that there exists broken rotor bar fault feature in power supply current signal, and thus, fault diagnosis of broken rotor bar in induction motor power supplied by a converter can be achieved.