Abstract: The information of primary knock-on atom of material under neutron radiation in nuclear reactors is the inputs for multi-scale material computational simulations. Two different computational methods for primary knock-on atom (PKA) simulation under neutron radiation, including scattering matrix transformation and Monte Carlo simulation, were investigated in this paper. The PKAs of Zr, Fe, W and SiC under the neutron radiation in pressurized water reactor (PWR) were simulated using these two methods. The energy spectrums of PKAs were attained and compared, which shows the good agreements between these two methods. Moreover, the Monte Carlo simulation method has advantages for considering the effects such as the thermal motion of target nuclides and the chemical bonds between nuclides. The research in this paper provides foundations of the follow-up molecular dynamics and multi-scale material simulations.