Abstract: The standard enthalpy, standard entropy, standard Gibbs free energies and equilibrium constants of reactions concerned in methane of hydrogen isotope exchange were calculated with the density functional theory (DFT) using B3′ exchange and LeeYangParr’s correlation functional (B3LYP) with 631G** basis set. The temperature is the key factor which affects the reaction thermodynamics. The higher temperature is propitious for the methane of hydrogen isotope exchange, however, the more carbon deposit is produced if the temperature is too high. A suitable reaction temperature is prerequisite for obtaining a higher yield.