Density functional theory (DFT) plane wave pseudopotential method was used to study the structural changes of diamond when hydrogen impurities were located at three different sites in the subsurface of hydrogen terminated diamond films, and the difficulty of hydrogen atom adsorption on the three kinds of diamond films. Meanwhile, the transition state search of surface activation reaction was carried out. All work is to explore the influence of hydrogen impurities in the subsurface of diamond films on surface activation during chemical vapor deposition(CVD). The results show that: during the growth process, the structure of diamond near hydrogen impurities in subsurface is distorted, and the surface structure of diamond has an effect on the degree of distortion. The adsorption energy of hydrogen atom on the three kinds of diamond films containing hydrogen impurities are little different from that of ideal diamond film. However, the energy barrier of the active sites generated is lower than that of the ideal diamond films, which is related to the phenomenon that the hydrogen impurities in the subsurface make the diamond films have P-type semiconductor characteristics. The results show that the formation rate of surface active sites can increases as hydrogen impurities entering the subsurface of the film in hydrogen rich reaction atmosphere.