Abstract: The surface strengthening of 45 steel was carried out by the ultrasonic surface rolling processing (USRP) technique. Then the influence of USRP on the tribological performance of the steel and the mechanism were studied by means of the surface morphology and surface microstructure observation, surface roughness and friction and wear performance tests. The results show that the surface roughness of the USRP specimen decreased from 3.2 μm of the untreated specimen to 0.23 μm; the microstructure was refined, the grain orientation tended to be randomly distributed and the high-angle grain boundary was observed; the microhardness at the surface was about 56% higher than that of the untreated specimen, and the thickness of the strengthening layer was up to 400 μm; the friction coefficient of the USRP specimen was lower than that of the untreated specimen and the wear loss was 1/4 of the untreated specimen. The surface materials of the untreated specimen showed a piece-like peeling during the wear process with the wear mechanism of adhesive wear. While on the wear surface of USRP specimen, the ploughing formed grooves were observed and the wear mechanism was abrasive wear.