Abstract: Nanocrystalline diamond films depict superior tribological properties indicated from low friction coefficient and high wear resistance. The system pressure is one of the important processing parameters to prepare nanocrystalline diamond films. In this paper, diamond films were deposited at different pressures, and the sample was analyzed by scanning electron microscopy(SEM) and Raman spectrum. By the hot-filament chemical vapor deposition technique, when the methane was superfluous, the nanocrystalline diamond films could be deposited at right pressure. Higher system pressure would hamper the nuclei and the growth of nanodiamond films, and lower system pressure would cause diamond films grains coarse. The mechanism by which system pressures have the effect on the growth of diamond films is that the movement of atom H changes at different pressure.