Abstract: This paper based on the analysis methods of material fracture morphology and metallography, first analyzes the main causes of the thread fracture problem of the active bevel gear shaft of the bus axle, pointing out that the stress concentration at the thread root and excessively high hardness, combined with the interaction of assembly clearance, are the main factors leading to the thread fracture of the bevel gear shaft. Then, targeted improvement measures are proposed from the aspects of thread processing technology and assembly. Finally, after practical verification, the thread fracture problem of the gear shaft has been effectively solved.