The synthesis process of solid TiC in thermal plasma was investigated theoretically by computing the equilibrium composition of the gas mixture containing titanium and chlorine (titanium as a reactant is assumed to be in the form of titanium tetrachloride) with argon, hydrogen and carbon (carbon as a reactant is assumed to be in the form of methane). The calculation was performed for the temperature range between 500 and 6000 K and the total pressure in the system of I bar. The fact that thermal plasma is plasma in (local) thermodynamic equilibrium made possible the theoretical determination (by employing the Gibbs free energy data for the compounds present in the system and assuming that the equilibrium of the system corresponds to its minimum energy state) of its equilibrium composition. From the calculated compositions of the investigated gas systems the temperature zones with saturated and/or oversaturated vapor of Ti, TiC and C were determined and the mechanism of the formation of TiC in solid state was proposed.