Abstract: The abnormal sound phenomenon of an engine idler bearing appeared at road test, the spalling failure was found on the surface of inner bearing race after dismantling. The failure cause of bearing was analyzed by macro examination, chemical composition analysis, hardness testing, metallographic examination, energy spectrum analysis and scanning electron microscopy(SEM)analysis. The results showed that, due to abnormal working conditions, the subsurface of the bearing inner ring raceway had occurred white organization variation, in operation the contact fatigue resulting in local area flaking. And the granular carbide aggregated distribution constituted ribbon segregation of inner bearing race material and coarse carbides, causing the mechanical properties of the steel, particularly fatigue properties significantly decreased, by abnormal impact loads and larger vibration, so the ribbon carbide segregation area and coarse carbides area were also easy to be the birthplace of fatigue peeling.