In this paper, the chemical reaction model in the growth of {100} orie nted CVD (chemical vapour deposition)diamond film is founded, and the growth mec hanisms of surface chemisorption are related to: (1) the BCN mechanism; (2) the dimer insertion; and (3) the trough insertion, in which the trough insertion mec hanism is in dominant. The growth process of (100) surface under this model is s imulated in atomic scale by using the modified KMC method, and the effect of sub strate temperature and CH3 concentration on film quality is provided. The result s show that this chemical reaction model can actually reveal the growth of {100} oriented CVD diamond film.