When an energetic particle interacts with a lattice atom, different processes would be initiated sequentially intime (up to 10?12 10?11 s)[1]. Except the mobile process of defects in the last step, the others are largely athermal.Thus, the formation and stability of defects produced by irradiation in metals depends on various parameters. Theeffect of temperature has been studied for years, especially by computers simulations for displacement cascade. Thehigher temperature is, the less stable Frenkel pairs (interstitial - vacancy) are left[2]. In addition to temperature,the strain or stress field would also be contributed to the formation of defects, since the formation energy is affectedby these fields. In this report, we firstly present the results of strain field effect on formation of different defectsand critical displacement energy. The discussion is then given in the end.