Abstract: In order to understand the cause of fracture failure of the workpiece used in bolt service for turnout, the broken bolts were detected, evaluated and analyzed by means of appearance inspection, physical and chemical testing （chemical analysis, hardness test, metallographic test） and fracture analysis. The results show that the failure mode of the bolt is bidirectional bending high cycle fatigue fracture, and the root cause of the fracture is the existence of decarburization layer at the thread, which seriously affects the fatigue resistance of the material.By analyzing the failure mechanisms of bolt fractures, valuable insights can be provided for the manufacturing processes and quality control of switch bolts, thereby enhancing their durability and reliability and reducing the risk of fractures.