With the advancement of power electronics technology, the new generation of high-frequency vehicle auxiliary converters with dual bridge series resonant DC-DC converter (DBSRC) as the core have developed rapidly and are gradually moving towards practicality. In order to improve the reliability of high-frequency auxiliary converter based on DBSRC, using operation mode analysis (OMA) to study the IGBT open circuit fault in DBSRC under phase-shifting closed-loop control first, the operating mechanism and characteristics of DBSRC after input and output side faults are analyzed and clarified. Second, a fault-tolerant operation strategy based on output power adjustment for high-frequency auxiliary converter is proposed for DBSRC IGBT open-circuit fault. It real-time monitors the input voltage of the auxiliary converter, and dynamically adjusts the output power, limiting the resonant current stress and resonant capacitor voltage stress to a safe threshold and achieving fault-tolerant operation, in the context that DBSRC topology and phase-shifting control method are retained. Finally, the simulation and experimental results verify the accuracy of the fault characterization and the effectiveness of the fault-tolerant operation strategy.