Computer simulation techniques in atom scale have now become so powerful that phenomena associated with irradiation damage effects in metals can be modelled with a high degree of realism. As a powerful tool, molecular dynamics (MD) is applied to study the displacement cascades initiated by the neutrons when they interact with matter. There exist a lot of inter-atomic potentials dedicated to bcc Fe and we choose the EAM potential. At first time PKAs (Primary knock-on atoms) knocked on a atom and send a part of energy to it what result displacement cascades. After about several ps, a lot of atoms are knocked to leave the equilibrium position and became self- interstitial atoms (SIAs). A lot of equilibrium position became vacancies. Some SIAs and vacancies form dumb-bells structure. Several vacancies or SIAs assembled the clusters. In other papers we haven’t found about the SIAs and vacancies can be assembled the SFT-like clusters in bcc Fe. In our study, we occasionally find SIAs can assemble to form the cluster in bcc Fe but need a higher energy. In our study, we choose the temperature from 100K to 600K, the energy from 100eV to 20keV. The particles scale is about 300 thousands. In a series of experimentation we find that as the temperature increase as the number of the SIAs and vacancies increase too. By the same token, as the energy increase we will find the same result.