Abstract: The scuffing failure reasons of connecting rod bearing shells of a diesel after a short time of running-in bench test were analyzed by macro,micro and chemical compositions analysis.The results show that scuffing failure of the connecting rod bearing shells was mainly caused by the non-compliance cleanliness.Combining the force situation,it was considered that the early wear was mainly because there were a lot of impurities in the oil which induced surface scratch of the connecting rod bearing shells.The damage of the lower shell was more serious because of its bad working condition,and particles falling from the lower shell accelerated the wear of the upper shell,which finally resulted in scuffing failure of the connecting rod bearing shells.