The paper presents the fabrication of Si3N4 nanowires prepared on Si substrate by plasma-enhanced chemical vapor deposition (PECVD) technology. The nanowires were formed using silane (SiH4) and nitrogen (N2) as reactive gases under the action of Fe catalysts. They are characteristics of superlong straight and flexural types observed by field emission scanning electron microscopy (FESEM). The former with a length of 3.96 mm has smooth surface and uniform diameter resulting from an orientation growth process, while the latter is 5.20 mm formed by two nanowires twisted together with a squeezing growth way. A growth model has been developed for the formation of the nanowires, and the growth mechanism of the nanowires has been discussed. The straight and flexural Si3N4 nanowires can be used as nano-scaled bridge, spring, and cantilever in the fabrication of nano-machine systems.