With the 3^#lithium Grease lubrication conditions, influence about 35 GrMo testing block with a sierses of different roughness on pair, friction and wear characteristics of GCr15 / 35 CrMo was studied. By means of scanning electron microscopy ( SEM) , the surface morphology of the worn test block with different roughness was analyzed. And combined contact condition of the 35 CrMo supporting shaft of beam pumping units and needle roller bearing without inner ring, the causes and mechanisms of the roughness on the friction pair were analyzed . The results show that: the surface roughness of the test block exists an optimal range, and the coefficient of friction and the wear rate is relatively small in this range. When the surface roughness of the test block is too high or too low, the wear rate is relatively more large. When the roughness is large,the mechanism of the damage to the test block is due to furrow injury.