In order to investigate the range of nucleation area of Si nanoparticles under different pressures, a single crystalline Si target with high resistivity is ablated by a XeCl excimer laser (wavelength 308 nm, laser fluence 3 J/cm2) in an ambient pressure range from 1 to 200 Pa of pure Ar gas. The Si nanocrystalline films are systemically deposited on glass or single crystalline Si substrates that are lined up at a distance of 2.0 cm under the ablation point. Raman and X-ray diffraction spectra indicate that the films are nanocrystalline. Scanning electron microscope images of the films show that the ambient pressure effect on the average size and the distributing range of Si nanoparticles on the substrate. According to the method of determining the location of nucleation area, it is found that the range of nucleation area of Si nanoparticles first broadens and then narrows with the increase of ambient pressure. The dynamics is analysed theoretically to explain the results.