In this study, molecular dynamics simulation method is used to investigate the interactions of Cl continuously bombarding a crystalline Si (100) surface in an incident energy range of 0.3—10 eV.The surface temperature is set to be 300 K for all the incident energies. The improved Tersoff-Brenner type potential is employed.The simulation results show that a Cl-rich reaction layer is formed on the surface due to Cl continuously bombarding. The SiCl group is the predominant species in the reaction layer.The thickness of the reaction layer increases with incident energy. The etching ratio increases with incident energy increasing. The main etching product is SiCl4 when the incident energies are 0.3, 1 and 5 eV, but it is SiClx(x<4) when the incident enery is 10 eV.With the incident energy increasing, the main etching mechanism changes from chemical etching to physical etching.