AISI 304L austenite stainless steel was irradiated by a high-current pulsed electron beam (HCPEB) source in different process. The deformation microstructures were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The relationship between stress characteristic and the microstructures has been established. The current numerical simulations of the thermal-mechanical process of HCPEB treatment were also reviewed comparing with the present experimental results. Our experimental results suggest that the value of the stress induced by HCPEB is between 10²–10³ MPa or even larger. This stress results in the change of microstructure of the irradiated material in deeper region beneath the surface. According to the experimental results, a new physical model of the thermal-stress process and related modification mechanism as a result of HCPEB irradiation has been developed.