During a repair welding process, the ultrasonic shot peening (USP) process can be used as the final finishing step. The aim is to introduce compressive residual stresses on the surface of the welded area in order to prevent the occurrence of cracking. Although the numerical simulation method is able to predict the state of residual stress in the peened part, the 3D models of the real USP process, in which many successive and shifted impacts take place, is very delicate and costly in terms of computing time and memory space required. In this paper, we propose a method based first on the calculation of the averaged inelastic strain tensor in a local representative area, and second on the transfer of this inelastic strain field in order to simulate the USP process. Experiments, similar to the "Almen test", are performed on a thin plate of Inconel 600. Numerical results in terms of distortions and residual stresses are compared with the experimental data.