Perovskite ferroelectrics have high endurance to radiation. In order to understand the mechanism at the atomic level, molecular dynamics simulation is applied to investigate the process of defects generation and displacement cascades in crystal. The calculated average threshold displacement energy of O, Ba and Ti atom is 53 eV, 70 eV, and 119 eV, respectively, so the number of O defects is larger than that of Ba and Ti defects. Furthermore, the simulations show that the initial movement direction of the primary knock-on atom (PKA) has significant influence on the number of defects because of different collision type (glancing collisions or direct knocks), and the number of Frenkel defects does not simply increase with increasing PKA energy due to the annealing effect. This investigation of the collision cascades is helpful to understand the radiation damage in crystal and may offer useful guidelines to the design and applications for the practical devices.