Abstract:The effect of the surface roughness and residual stress of 40 Cr by ultrasonic light finishing and reinforcing process was studied. It was found in experiment that the initial roughness of shaft parts was able to be reduced from 2.48 μm to 0.04 μm. The blindhole method was adopted to test the surface residual stress. The results show that the whole surface residual stress of untreated part is tensile stress. Among which, the value of σ1 is stable at around 30 MPa, which is tensile stress. With the increasing of layer depth, σ2 becomes from residual compressive stress to residual tensile stress, which is under 10 MPa. The surface residual stresses of treated part are all compressive stress. The influence depth of material by the process is from 1 to 1.5 mm. The values of principal stress σ1 and σ2 are stable between 160 and 170 MPa. With the increasing of drilling depth, the residual compressive stress tested value has a tendency to slightly lower.