Traction inverter is one of the most important part of traction drive system in the train, and the reliability of the traction inverter affects the normal operation of the entire train directly. In this paper operated the accelerated test on IGBT module of TNG15 type traction inverters in the Beijing metro firstly. Then calculated the failure rate of IGBT module through Arrhenius model, for the coupling element, used small-sample method of reliability evaluation to calculate the failure rate of it. Combined with the reliability parameters of other electronic components in the traction inverters, the qualitative analysis and did the quantitative analysis of traction inverter system through GO methodology. GO method is widely used in the defense industry and other large systems, but it is rarely involved in the small systems. This paper provides a method for the reliability assessment of traction inverter, and it provides an idea for the reliability assessment of the other converter components in the train traction transmission system.