Abstract: Polystyrene-divinylbenzene (SDB) is an important hydrophobic catalyst in gas-liquid exchange reactions to separate hydrogenous isotopes. Using method of B3P86 density functional theory and basis set 6-311G, the ground electronic state and its energy, dissociation energy, and geometrical parameters of styrene which acts as the hydrophobic functional fragment in SDB were computed. The internal energy, enthalpy, and entropy of H2 and D2 referred to the displacement reaction were calculated as well. Employing electron-vibration approximation theory, the enthalpy and entropy of styrene in solid state before and after displacement reactions were also calculated. Then the changes of enthalpy, entropy and Gibbs free energy, the reactive equilibrium constant, and the gas pressure ratio were all obtained. The results indicate the reaction of deuterium displacing hydrogen in SDB is possible to occur to a low level and will become more difficult with increasing temperature, and it occurs more easily in phenyl than in vinyl.