Radiation displacement effect is studied using shell model molecular dynamics simulations. Using oxygen atom as a primary knock-on atom, the creation and the evolution of various defects in the system corresponding to the primary knock-on atom(PKA) energy of 1 keV are studied. The results show that a largest number of defects are created when the incidence is along the 001direction. Among all the defect species, oxygen atom defects are dominant, and its concentration reaches 80%. The creation of defects does not change the spontaneous polarization of the system significantly, and the polarization reversal also changes little. Defect migration is observed under an applied electric field.