This paper proposed an electro-thermal coupling finite element method for the mechanism analysis of the IGBT collector-emitter voltage increase due to the bond wire degradation. Experimental results show that bond wire degradation may lead to the increase of bond wire contact resistance, which is generally seen as the main reason for the increase of IGBT collector-emitter voltage. However, due to the forward voltage drop in the IGBT chip contributes to the most part of the collector-emitter voltage, the electro-thermal simulation results find that the increased chip temperature is the primary reason for the increase of collector-emitter voltage after the degradation of the bond wires. Finally, the mechanism analysis method presented in this paper is verified by accelerated experiments with Starpower GD50HFL120C1S IGBT modules.