To study the effect of surface characteristics and fatigue properties of 45# steel by ultrasonic surface rolling processed. The 45# steel was treated by USRP equipment, and the surface characteristics, state and microstructure of the before and after specimens were observed and analyzed by means of the corresponding measurement equipment. The fatigue properties of the specimens were measured by the rotary bending fatigue test, through the bruceton method to obtain the assessment of fatigue limits. After USRP treatment, the surface roughness Ra decreased from the previous 3.2 μm to 0.23 μm; grain refinement, the grain orientation tends to random distribution; the micro-hardness of the surface layer was about 56% higher than that of the heart; the thickness of the strengthening layer was up to 400 μm; the maximum residual compressive stress increased from ?180 MPa to ?532 MPa before the treatment and the fatigue limit of USRP specimens increased from 296 MPa to 403 MPa. Through USRP technology, the surface characteristics and surface properties of the 45# steel specimens were improved. The improvement of fatigue properties was mainly due to the combined effect of low surface roughness, grain refinement, the increase of the microhardness and residual compressive stress.