“In response to the safety hazards caused by the failure of the mode switch in the hybrid traction system under extreme working conditions, the article first analyzes the structural principle and failure mechanism of the switch; secondly, deeply studies the fault characteristics of the mode switch in different failure states and its impact on system safety, and proposes a set of fault diagnosis and protection methods to ensure the safe operation of the hybrid traction system; finally, the accuracy and effectiveness of the method are verified through simulation. The method proposed in the article can provide reference for the design of subsequent hybrid traction systems. Experts conduct in-depth research and propose solutions to provide guarantees for the safe operation of the system.”