Abstract: The crack of brake disc bolt of high-speed train was directly related to the driving safety of the train. The cracks of the brake disc bolt were usually found during regular maintenance. Most analysis were conducted by combining physical and chemical testing and fracture analysis, while few studies combined the service environment and service state of bolts was used to analyze the formation mechanism of cracks. The finite element model was established by ABAQUS to analyze the stress field and strain field of the bolt. The simulation results were consistent with the actual fracture condition.The stress concentration and fracture were located at the bottom of the first thread meshed between the nut and the bolt. The root cause of bolt fracture was that the fasteners were not tightly fixed due to insufficient pre tightening force of fastener assembly. The research results can provide help for the service of bolts.