Abstract: The main wear mechanism of timing chain under oil lubrication is fatigue wear and the formation and propagation of crack are the dominant factors governing the fatigue life of the chain. That of the transmission chain under periodical lubrication of oil brushing or oil dropping is abrasive wear, accompanied with fatigue wear. The structure and characteristics of carburized layer and center of pin and bush play an important role in governing the wear resistance of the chains. Medium carbon hardened tempered steel after nitrocarburization has well dispersed granulated carbide superficial layer and tempered trooslite core, hence demonstrates the comprehensive mechanical features of high wear resistance, high strength and toughness, and high resistance to plastic deformation.