The nanocrystal silicon films were prepared by using a pulsed laser to ablate a high-resistivity single crystalline Si target in an ambient pressure range of 0.01-0.5 Pa of pure argon gas. An argon gas flow is introduced in the horizontal direction of the ablation point in an axial range of 2 cm. Nanocrystal Si films are deposited on glass or single crystalline (111) Si substrates placed at a distance of 1 cm below the nozzle. Then the same device is used to prepare the ranocrystal Si films at a pressure of 0.08 Pa with gas flow being, respectively, 0, 2.5, 5, 7.5, 10 sccm. The morphologies and microstructurs of the samples are characterized by atomic force microscopy (AFM), X-ray diffraction (XRD) and Raman scattering. The results show that the Si nanocrystal threshold pressure is 0.1 Pa without gasflow, and 0.05 Pa with gasflow. The size of Si nanocrystal decreases as the gasflow increases.