The radio frequency (r. f.) magnetron sputtering was used for preparing silicon-rich silicon nitride films deposited on polished Si substrates at 80 degrees C substrate temperature. The high-purity Ar was used as a sputtering gas and the high-purity N2 as a reactive gas. The silicon nitride films with different Si-rich degrees were obtained by changing the flow ratio of Ar/N2, and subsequently the samples were annealed at a high temperature in pure N2 ambience. The influence of annealing on the properties of films was investigated by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and photoluminescence (PL). The appearance of Si-N bonds can be confirmed by the XPS, from which the ratio of Si/N can be rough estimated. Therefore, the XPS reveals that the sample before annealing has a high content of Si which is the premise to come into being nanometer Si. However, the PL peak of the films before annealing in the visible light region was not observed obviously. The XRD results indicate that the presence of Si clusters buried in the films after annealing was confirmed by two novel diffraction peaks, which are related to nanometer Si. As the flow ratio of Ar/N2 decreased, the emission intensity of PL peak in the visible light region was enhanced, accompanied with a blue-shift of emission peak. According to the quantum confinement effect, the blue-shift of PL peak should be attributed to the enlarged band gap of Si clusters in the sample, and the increased intensity of the PL peak turns out to be due to the size of nanometer Si. The two important factors of annealing treatment and flow ratio of Ar/N2 were studied, which have an intimate connection with emitting mechanism in PL. The blue-shift of PL peak caused by nanometer Si embodied in the silicon nitride thin films depends on the sputtering condition, such as flow ratio, deposition temperature and sputtering pressure.