Abstract: ［Objective］ Axlebox bearing failures in metro vehicles can lead to wheelset seizing, resulting in scenarios ranging from passenger evacuation and vehicle rescue to severe incidents such as interval blockages or even derailments. These failures significantly compromise vehicle service performance and operational safety. A particular metro line experiences two instances of bearing failure during operation, necessitating an in-depth analysis of the root causes. ［Method］ A detailed sampling analysis is conducted on the failure axlebox bearing components. Retrospective checking of the maintenance and operational processes are traced, and tracking tests are conducted on vibration, temperature, and imaging of bearings from the same batch under same operating conditions. Additionally, a systematic analysis is conducted on the installation structure and fitting dimensions of the bearings and the auxiliary components. ［Result & Conclusion］ The analysis results reveal that the chamfering of the insulation board in the axle-end grounding device exceeds the upper design limit, leading to poor sealing at the joint surface. During vehicle operation, air-conditioning condensate infiltrates the axlebox bearings along the joint surface, causing emulsification and degradation of the lubricant, which results in reduced lubrication performance, bearing overheating and eventual bearing failure.