There is an increased demand of the explanation of the thin film fabrication mechanism, especially for thickness uniformity, film quality and product yield. Any modeling of the mechanism requires a sufficient knowledge of the basic mechanism of interaction and reaction of the particles with the substrate. As a first step, here, the model of silicon thin film formation under low-pressure CVD is considered. Silicon film formation and growth on a clean solid substrate is simulated applying the molecular dynamics and chemical reaction principles. The analyzed domain is enclosed in a hexagonal box which has periodic boundary conditions and a different flow energy of the particle. The atom surface adsorption and inelastic collision are discussed considering the exchange energy between the particles and the surface. In order to provide a well visualized description, a graphics program is made to show the particle movement and the film fabricating process in three dimensions. The present simulation is advantageous to the macro-understanding of the thin film formation mechanism and to fabricating the machine design with optimum control.