Abstract: The high-altitude environment severely challenges the insulation reliability of IGBT modules. A low-pressure IGBT partial discharge detection platform was built to explore the partial discharge characteristics of IGBT modules under high altitude conditions. The partial discharge inception voltage (PDIV), extinction voltage (PDEV), maximum apparent charge, average charge, discharge pulse repetition rate, and phase resolved partial discharge (PRPD) were measured in the pressure range of 20~100 kPa under AC power frequency voltage. The results show that the partial discharge phenomenon of the IGBT module is not obvious at 70~100 kPa pressure and obvious partial discharge occurs at 60 kPa. The discharge position is mainly concentrated before and after the voltage polarity reversal, and as the pressure further decreases, the phase of PRPD gradually widens, and the discharge amount and discharge repetition rate increase significantly. Then, the finite element analysis method is used to analyze the field intensity distribution of the IGBT module at the cut-off time. It is found that the electric field at the junction of the IGBT module bonding wire pin, silica gel, and chip, as well as the junction of copper plate, silica gel, and ceramic plate. is the most concentrated. There are many micro air gap channels at the interface of different dielectric materials, an important path for the external pressure change to transmit to the IGBT module. The field strength in the micro air gap channel is more concentrated, and the electron-free path in the micro air gap channel is larger under low pressure, which makes the partial discharge more intense. Different polar charges gradually accumulate on both sides of the micro-air gap channel electrode and silica gel. When the polarity of the applied voltage is reversed, it is superimposed with the space charge field strength, resulting in abnormal severe partial discharge. The research results can provide a reference for the insulation design and safe and reliable operation of IGBT modules under low-pressure conditions.