Porous silicon can be fabricated by laser irradiation and annealing. The center wavelength of photoluminescence （PL） band is pinned in the region of 700—780 nm and its intensity increases obviously after oxidation of the sample. It was found that the PL intensity changes with time of laser irradiation and annealing. Calculation shows that some localized states appear in the band gap of the smaller nanocrystal when SiO bonds or Si—O—Si bonds are passivated on the surface. It was discovered that the number of SiO bonds or Si—O—Si bonds, which are related to irradiation and annealing time, obviously affects the generation of localized gap states.