The electric energy, nuclear energy and entropy of H₂O, D₂O, T₂O, H₂, D₂, T₂, O₂ were calculated under the dipole electric field from －0.05 to 0.05 a.u., employing B3P86 method of the density functional theory with basis sets 6-311＋＋G(3df, 3pf), by further calculating the enthalpy change ΔH, entropy change ΔS, Gibbs function change ΔG in the reaction of H₂O(g)→H₂(g)＋O₂(g), D₂O(g)→D₂(g)＋O₂(g), T₂O(g)→T₂(g)＋O₂(g), the reversible decomposition voltage E_r of H₂O, D₂O, T₂O were obtained. The results show that the presence of dipole electric field will evidently influence the change of Gibbs free energy ΔG and the reversible decomposition voltage E_r of H₂O, D₂O, T₂O, for example, when the positive dipole electric field increases, the Gibbs free energy change ΔG and reversible decomposition voltage E_r tend to a linear increase; but when the negative dipole electric field increases, the Gibbs free energy change ΔG and reversible decomposition voltage E_r tend to a linear decrease, under the same dipole electric field, Gibbs free energy change ΔG and reversible decomposition voltage E_r increase with the order of H₂O, D₂O, T₂O.