The method of preparation of hydrogenated silicon oxycarbonitride films with variable composition SiC x N y O z : H by the plasma chemical vapor decomposition of a volatile organosilicon compound, 1,1,1,3,3,3-hexamethyldisilazane (enhanced to IUPAC, bis(trimethylsilyl)amine) in a gas phase containing nitrogen and oxygen in the temperature range of 373–973 K has been developed. It has been shown that nitrogen and oxygen provide the decrease in carbon content in films due to gas-phase reaction giving volatile products (CN)2, CH4, CO, and H2(H). The obtained SiC x N y O z : H films are nanocomposite, in the amorphous part of which the nanocrystals are distributed, which belong to the determined phases of the Si-C-N system, namely, α-Si3N4, α-Si3 − x C x N4, and graphite.