The surface of austenitic stainless steel irradiated by energetic beams was studied by molecular dynamics (MD). Thermal spike model was used to simulate the energy transferring process under irradiation. By analyzing the energy distribution and the atomic motion, the mechanism of energy consumption was determined. One part of energy was consumed by the atoms on the surface through evaporation and heat conduction. The other part transferred deep inside the matrix in shock wave form. The smooth process of surface resulted from the decrease of the evaporation strength and the readsorption processing.