Hydrogenated nano-crystalline silicon (nc-Si:H) thin films were prepared by plasma enhanced chemical vapor deposition (PECVD). The variation in the crystallinity, nano-structure and optical characteristics of the nc-Si:H films with deposition variables such as reaction gas, post-deposition heat-treatment and deposition time were investigated; the relationship between the optical nano-structural features of the nc-Si:H films was discussed. The intensity of the PL peak, observed at about ~ 480 nm region, increased with the amount of reaction gas as well as deposition time. On the other hand, PL peaks appear at ~ 580 nm region when the sample was annealed in vacuum, and the intensity of the peaks increased with increasing the annealing time. It's believed that radiative recombination occurred due to the defects of SiO x in the film.