In He, Ne or Ar gas under a deposition pressure of 10Pa, nanocrystalline silicon films were prepared by pulsed laser ablation, which the deposition time was 5, 7, 13, 15, 69 and 350min, respectively. A Lambda Pyhsik XeCl excimer laser (wavelength 308nm, pulse duration 15ns, laser fluence 4J/cm2, repetition rate 1Hz) was used, and the distance between Si target and the substrate was 3cm. The Raman spectra indicate that the films are nanocrystalline. Scanning electron microscopy images show that the discrete nanoparticles are first formed, more and more nanoparticles are obtained with increasing of deposition time, and then some nanoparticles start to aggregate and form continuous film, and finally the film ruptures due to the stress. It is the complicated interaction between nanoparticles as-formed in the film and those produced subsequently to lead to the phenomena mentioned above. The morphology of the films deposited in different ambient gases is compared. The result shows that aggregation between nanoparticles, film-formation and rupture take place in a lighter gas earlier than those in a heavier gas. This is related to the different growing rate of the films deposited in different gases.