A method utilizes easily obtained carbon as carbon source for sintering, followed by high energy ball milling process with planetary ball mill for high energy homogenous mixing of the carbon source, solvent and nano-level silicon dioxide powder, along with a high energy ball milling process repeatedly performed using different sized ball mill beads, so as to formulate a spray granulation slurry with the optimal viscosity, to complete the process of micronization of carbon source evenly encapsulated by silicon dioxide powders. The optimal ratio of C/SiO2 is 1-2.5 to produce a spherical silicon dioxide powder (40-50 μm) evenly encapsulated by the carbon source. The powder is then subjected to a high temperature (1450□) sintering process under nitrogen gas. Lastly, the sintered silicon nitride powder is subjected to homogenizing carbon removal process in a rotational high temperature furnace to complete the fabricating process.