Molecular modification methods can directly eliminate the influence of unstable groups on the properties of natural ester insulating oils. In order to verify the modification effect, we will explore the microscopic mechanism of the difference in the properties of insulating oils before and after the structural modification from the atomic molecular level. The TME-C ₁₀ and GT molecules of electronic structure properties have been calculated using density-functional theory, such as molecular orbital and density of states, electronic excitation features, electron affinity potentials, electron ionization energies, UV/Vis spectrum, molecular vibration and IR spectrum and so on. Additionally the polarity profiles and dielectric strengths of the two molecular systems with changes in electric field were also discussed. The results indicate that the electronic behavior of the TME-C ₁₀ molecule is related to the ester group in its structure, while the GT molecule is more affected by the unsaturated C=C double bond, which leads to the two molecular systems having different electronic transitions, and , respectively. The HOMO orbital energy levels, electron transition energies, and ionization energies of the GT molecule are smaller than those of the TME-C ₁₀ molecule are also due to the influence of the different functional groups. Under the influence of the ester group, it is found that the dipole moment of TME-C ₁₀ molecule is larger in the basal state in the vibration analysis, and further comparing and analyzing the molecular polarity of the two systems under the action of the external electric field, it is found that GT molecules with smaller dipole moments in the basal state are more easily polarized with the change of the electric field strength, and it is possible to judge that the dielectric properties of the modified TME-C ₁₀ are better in combination with the relevant calculated parameters.