<p>Brake disc bolts are pivotal for disc connection and braking safety of high-speed trains. However, existing research lacks an in-depth analysis of thread stress distribution and practical solutions for reducing bolt bending loads. To address this, the current study commences at the material level of failed bolts, utilizing characterization techniques to elucidate the failure mechanisms and modes. Concurrently, finite element method (FEM) is employed to visualize stress distribution, providing a mechanical rationale for structural optimization. Results indicate that the primary failure mode is fatigue fracture, with cracks initiating at the first working thread root and the bolt head. FEM analysis reveals that this fatigue fracture is attributable to pre-tightening-induced interference between the bolt head and hub, which leads to significant radial deformation and bending stress. Accordingly, an optimized bolt structure is proposed, incorporating a thickened shank at the hub/spacer holes, extended length, and supplementary sleeves. Simulation results demonstrate that the new design substantially reduces bending moments and radial deformation, effectively alleviating stress concentration and extending service life.</p>