Abstract: A universal shaft cross pin fractured during the operation of the locomotive. The fracture cause was analyzed by means of macroscopic observation, chemical composition analysis, hardness test, metallographic examination and scanning electron microscope analysis. The results show that the poor quenched martensite structure and large size MnS inclusions reduced the fatigue resistance of the chamfered part of the cross pin. Under the action of alternating stress, the fatigue fracture of the cross pin occurred.