Abstract: As the intermediate layer between GaN and diamond heterostructures, SiN_x is not only the protective layer of the underlying GaN material, but also the nucleation and growth layer of the upper diamond.Therefore, the SiN_x dielec-tric layer is of great significance for synthesizing high-quality diamond on the GaN surface.The research uses low pres-sure chemical vapor deposition(LPCVD) and magnetron sputtering(MS) methods to prepare silicon nitride dielectric layers on silicon-based gallium nitride substrates.Analyses of the surface morphology, crystal structure, and surface func-tional groups of SiN_x films were performed using scanning electron microscopy, Fourier transform red spectroscopy, X-ray diffraction, and laser Raman spectroscopy.The results show that the diamond/gallium nitride interface is complete and dense after seed crystal seeding and diamond nucleation in the amorphous silicon nitride dielectric layer plated by LPCVD, while the dielectric layer prepared by magnetron has crystalline characteristics., the corresponding interface will have obvious etching pits.The deposition method of the dielectric layer will affect the crystal structure and microscopic morphology of the SiN_x film.The high-density amorphous structure is more conducive to the rapid nucleation and growth of the diamond layer, which is more favorable for the construction of GaN-on-diamond structures.