Hierarchical modeling based on atomistic and continuum simulations were established to describe the fundamental characteristics of plastic deformation in irradiated materials. Typical irradiation defects of a self-interstitial atom (SIA) loop and vacancy loop are considered. At first atomic models, including a SIA loop and a vacancy as well as a straight dislocation loop in single crystals were constructed. Constant strain is applied to each model and the equilibrium configuration under deformation is calculated by a molecular statics simulation. Maximum shear stresses in various radii of irradiated defects are stored in a database for the continuum mechanics analysis. Then local interaction events between glide dislocation and irradiation defects were introduced through crystal plasticity finite element analysis. In this model the effect of radiation hardening was considered by referring to the experiment. We found that softening after the first yield event is caused by annihilation of irradiation defects resulting from unfaulting of the radiation defects.