The present work makes a contribution to thermodynamic study for the separation of tritium by CECE method from D₂-heavy water involving tritium.The reversible decomposition voltages of H₂O,HDO,D₂O,DTO and T₂O have been calculated and the difference of decomposition voltage for H₂O andT₂O is 0.047 V. Therefore,the electrolytic volt of heavy water must be less 0.047 V than that of H₂O. The functional relations of vapor pressure and vaporization heat with temperature from 0~100 ℃ for these five kinds of hydrogen-isotope water are derived. The equilibrium constants for reaction (19-1) and reaction (19-2) are also evaluated and both are quite small. Therefore,it is impossible to realize the two reactions in static system,however,it is possible to realize them in flow system. The most disadvantage for CECE method is the rather poor selectivity,the exploration is try to under way.