Abstract: The displacement cascades in α-iron caused by 1.50 keV primary knock-on atoms (PKA) at temperature range from 500 to 700 K were simulated by molecular dynamics method in this work. The evolution of defects induced by displacement cascades was studied in detail, such as the structure of defects, the statistic of survival defects and clustered defects at different PKA energy stages and temperatures. The quantitative relationship between the energy of PKA (E_PKA) at different stages and the number of survival Frenkel pairs (N_FP) was analyzed. It is concluded that the structure of defects induced by displacement cascades is related to the size of defects, which could guide the construction of clusters, dislocation loops and other defects. The retention of large clusters would significantly improve the N_FP when E_PKA is high. As a result, the N_FP-E_PKA fitting curve’s exponents at different PKA energy stages are quite different, and the variation of fitting curve’s exponents will be reduced with the increase of temperature.