Abstract: Based on a case of metro vehicle bearing positioning pin fracture failure, the root cause for the problem is analyzed. The insufficient clamping force from the bearing outer ring and insufficient strength of bearing positioning pin are identified as the main factors accounting for positioning pin fracture. Through structure analysis and experimental test, solutions for the positioning pin fracture failure are discussed, which propose the adoption of foam rubber for axle box back cover gasket to fundamentally solve the problem of insufficient clamping force from the bearing outer ring; and the optimization of welding method for positioning pin by using the Tig (tungsten insert gas) remelting welding of four seams. Test result indicates that the above measures can solve the problem of vehicle bearing positioning pin fracture failure.