In this paper, silicon nitride deposition process was carried out by using plasma enhanced chemical vapor deposition (PECVD). The influence of processing parameters on PECVD film properties were discussed. In conclusion, it was convenient to obtain low stress SiNx film by controlling the switching time of high and low frequencies respectively; dense high quality SiNx films with low tensile stress can be grown. The results showed that PECVD silicon nitride had the characteristics of small thickness deviation and stable refractive index, which establishes a foundation for its application in optics.