The GaN epilayers were grown on Si(111) substrates via combining the techniques of AlN buffer, the graded AlGaN structure and the Si xNy interlayer by metalorganic chemical vapor deposition. The SixNy interlayers with various growth times of 0-60 s were introduced into the growth of GaN epilayers. To thoroughly realize the growth evolution of SixNy, measurements of atomic force microscopy, field emission scanning electron microscopy and nano-Auger electron spectroscopy were performed. From the measurement by transmission electron microscopy, it can be proven that nanocrystalline SixNy is preferentially located at the dislocation cores and pits during the growth process. For the fabrication of GaN/graded AlGaN/AlN/Si, the full width at half maximum of the X-ray diffraction rocking curve at the GaN(102) plane was reduced effectively from 965 to 771 arcsec by inserting SixNy into the GaN epilayer, which resulted from the bending and annihilation of dislocations.