A thermodynamic calculation on the chemical vapor deposition of the SiCl4–NH3–CH4–H2–Ar system was performed using the FactSage thermochemical software databases. Predominant condensed phases at equilibrium were SiC, Si3N4, graphite, and Si. The equilibrium conditions for the deposition of condensed phases in this system were determined as a function of the deposition temperature, dilution ratio (δ), and reactant ratios of CH4/SiCl4 and NH3/SiCl4. The CVD phase diagrams were used to understand the reactions occurring during the formation of Si–C–N from the gas species and determine the area of SiC–Si3N4. The concentration of condensed-phase products was used to determine the deposition conditions of CVD SiC–Si3N4. The present work was helpful for further experimental investigation on CVD Si–C–N.