Abstract: The degradation of 2-chlorophenol and 4-chlorophenol molecules is studied using density functional theory with B3LYP/6–31G++(d, p) and B3LYP/6–31G (d, p) as the basis sets, respectively. An electric field (–0.025 – 0.025 a.u.) is applied along the x -axis direction. The ground state bond length, dipole moment, energy, orbital energy level, energy gap, infrared spectrum, vibration, and excited states of the two molecules are calculated. The results show that after the external electric field is applied along the C→Cl direction of the two molecules, the C–Cl bond lengths of the molecule increases gradually, the dipole moment decreases first and then increases, and the total energy and energy gap increase first and then decrease. From the results of infrared spectroscopy, it is concluded that the C–Cl bond stretching vibrational frequencies has a red corresponding shift and the absorption peak increases; the applied electric field has different effects on the excitation energy, wavelength and oscillator strength of each excited state of the two molecules. Along the direction of C→Cl bond, with the increase of external electric field, the molecular barrier gradually decreases. When the external electric field applied to 2–chlorophenol and 4–chlorophenol molecules is –0.025 a.u. and 0.025 a.u., respectively, the barrier almost disappears and the molecules gradually dissociate. The results can provide a reference for studying the dissociation of 2–chlorophenol and 4–chlorophenol molecules with external electric field.