Abstract: The effect of processing passes of USRP on the surface roughness, microstructure and residual stress distribution of M50 steel was analyzed using three-dimensional microscopy, FESEM, X-ray stress analyzer, etc. The fatigue and corrosion behaviors of M50 steel in different treating states were evaluated through rotating-bending fatigue tests and electrochemical tests, and the relevant mechanisms were explored. The results show that M50 steel undergoes cumulative plastic deformation during USRP process, the surface roughness is reduced, the surface grains are refined and a certain degree of residual compressive stress is introduced, which together improve the fatigue resistance of M50 steel. Increasing the processing passes can deepen the plastic deformation layer and improve the surface hardening effect, but the fatigue life of M50 steel does not increase with the increase of processing passes. Ten-passes processing under 1000 N can provide better fatigue resistance for M50 steel, the fatigue crack of the sample initiates in the subsurface away from the surface of 157 μm at 1000 MPa, and the fatigue life is up to 11.017 million cycles and nearly 5 times that of untreated sample. In addition, USRP processing can endow M50 steel with better passivation performance and improve its corrosion resistance, especially for the samples treated with 10 passes, its corrosion current density is the lowest and only 4.10 μA/cm².