Density functional theory (DFT) and time-dependent density functional theory (TDDFT) at the B3LYP/6-311+G(d, p) level were used to calculate and optimize the physical characteristics of 4-bromophenol under the different electric fields, including the bond length, bond angle, total energy, dipole moment, energy gap, infrared spectrum, dissociation properties, and excited state. The results revealed a significant change in the molecular structure of 4-bromophenol under an external electric field (0-0.03 a.u.). The molecular C—Br bond length, O—H bond length, and dipole moment increased gradually with increasing external electric field, while the C—O bond length, total energy, and energy gap decreased gradually. The four absorption peaks of the molecular infrared spectrum showed a red shift. Simultaneously, the first 10 excited states also showed a red shift. When the external electric field intensity was 0.03 a.u., the potential barrier disappeared, and molecular dissociation was observed.