A high frequency auxiliary converter module applied to the auxiliary converter system of 400 km/h high speed permanent magnet EMU was proposed. TLbuck transform, LLC resonance transform and three-phase inverter function were integrated in the module, which involved a variety of IGBT devices with different voltage levels, and solved the problem of voltage withstand of low-voltage devices under high-voltage conditions, suiting AC and DC power supply. The insulation design, overall structure design, heat dissipation design, drive control scheme was described, which was verified through simulation and test.