P-dibromobenzene (C6H4Br2) has a wide range of applications in the chemical industry, but it is also one of the organic pollutants that threaten the ozone layer. The study of the dissociation characteristic of the molecule under an external electric field has important reference value for protecting the ozone layer. Under the action of different external electric fields (-0.025~0.025 a. u.), the p-dibromobenzene molecule is optimized based on B3LYP/6-311+G(d,p) based on density functional theory (DFT), the ground state geometric structure is computed. They are then using the Time-dependent density functional theory (TD-DFT) and B3LYP/6-311+G(d,p) basis set to calculate the ultraviolet absorption spectrum of the p-dibromobenzene molecule to guess the dissociation property of the molecule. Finally, scanning the potential energy of the two C-Br bonds of the molecule gave direct evidence of the dissociation property of the p-dibromobenzene molecule. Studies have shown that under the action of an external electric field, the ground state geometric structure, spectral characteristics, potential energy curve and potential energy surface of p-dibromobenzene molecules have undergone major changes. With the increase of the external electric field, the 3C-12Br bond length and total energy of the molecular system of p-dibromobenzene gradually decrease, and the 6C-11Br bond length and dipole moment gradually increase; the increase of the 6C-11Br bond length indicates that the 6C-11Br bond energy of p-dibromobenzene molecule is reduced, and the 6C-11Br bond is the easiest to break. The energy gap first increases and then decreases with the increase of the external electric field. The decrease in the energy gap indicates that the molecule is more prone to chemical reactions. The peak intensity at the stretching vibration of the C-Br bond gradually decreases. The peak intensity at the stretching vibration of the C-Br bond gradually decreased, and the absorption peak of the ultraviolet absorption spectrum increased slightly at first and then decreased abruptly. The energy-enhancing properties indicate that the vibrations intensify, and the chemical bonds become active. The 3C-12Br bond of the p-dibromobenzene molecule was scanned under an external electric field, and the potential energy curve of the 3C-12Br bond of the molecule was obtained. When the intensity of the external electric field is -0.02 a.u., the highest energy of the right barrier of the molecule is the same as the lowest energy. Flat, the molecular 3C-12Br bond is broken; continue to scan the potential energy of 6C-11Br under this electric field strength, the molecular 6C-11Br bond is broken, so the p-dibromobenzene molecule will gradually decompose the separation phenomenon. Under the action of an external electric field, scan the two C-Br bonds of p-dibromobenzene simultaneously to obtain the molecule’s potential energy surface. When the external electric field intensity is 0.02 a.u., the diagonal potential energy of the potential energy surface decreases, and another dissociation channel appears. Therefore, synergistic dissociation of p-dibromobenzene molecules may occur. These results provide data guarantee for the experimental study of the degradation mechanism of p-dibromobenzene molecules in an external electric field and have important reference significance for the study of the dissociation characteristics of the molecular system.