A thermodynamic calculation on the chemical vapor deposition of the SiCl4NH3CH4H2Ar 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 (), and reactant ratios of CH4/SiCl4 and NH3/SiCl4. The CVD phase diagrams were used to understand the reactions occurring during the formation of SiCN from the gas species and determine the area of SiCSi3N4. The concentration of condensed-phase products was used to determine the deposition conditions of CVD SiCSi3N4. The present work was helpful for further experimental investigation on CVD SiCN.