Abstract: Surface roughness is an important index of surface integrity,which has a significant effect on the performance of mechanical parts.Pre-stress hardening grinding test was carried out on 40 Cr workpiece,during which characteristics and influence factors of surface roughness were studied.The surface roughness of initial,middle and final sections of the workpiece was respectively measured.Resultsshowed that the surface roughness of the workpiece was not uniform along the surface,and that it assumed a gradually increasing trend from initial section to the final.As pre-stress remained constant,the surface roughness of the workpiece increased gradually with the increase of cutting depth.However,as cutting depth remained constant,with the increase of pre-stress,the surface roughness decreased but the surface integrity of the workpiece increased.