In order to accurately evaluate the health level of insulated gate bipolar transistor (IGBT), detect and replace the defective IGBT modules timely, and improve the reliability of power converter, a novel prognostic method for defects inside IGBT module based on the voltage drop of bond wires is presented in this paper with principle and characteristic. The ageing state of bond wires inside IGBT module is diagnosed by the changes of equivalent voltage drop of bond wires on a single chip, and then judge the health level of IGBT module. Experiment result shows that condition monitoring for defects inside IGBT modules based on voltage drop of bond wires can accurately identify the ageing process of bond wires. This method not only diagnoses the defect that all bond wires liftoff on one chip, but also recognizes the condition that part of bond wires liftoff on one chip. It has been greatly improved in terms of accuracy compared with the condition monitoring method by the use of gate signal. This method provides a theoretical support for the maintenance of power converter and can reduce the system maintenance costs.