A thin film including β-silicon carbide was synthesized by a reaction of silicon monoxide gas and carbon source derived from polyimide film (PIF) at 1400°, 1500°, 1600°, 1700° and 1800°C. Formation mechanism of the SiC film was investigated thermodynamically and kinetically through the relationships among the conversion ratio of SiC, synthesis temperature and time. The formation processes were simulated based on the calculation of differential equations concerning thermodynamic and kinetic constants of 7 chemical equations. The sample obtained had a film shape similar to that of the carbon source film. The results of the time dependence curves of the conversion ratio of SiC calculated from 7 chemical equations, 14 rate constants, 2 diffusion constants, 10 chemical species and 10 differential equations are in good agreement with the experimental results of the SiC conversion ratio as a function of synthesis time. The calculation results of solving each constant suggest that the formation processes of SiC are "rate-controlled reaction at the interface" at the initial stage of the reaction, and then they gradually change to "diffusion-controlling reaction in the reacted region". In the long term synthesis, we recognized that the waste SiO with non-stoichiometric oxygen can also be used as a silicon source.