Abstract: Utilizing density function theory (DFT), the structure, spectrum and dissociation properties of CH₂BrCl molecules are studied in the external electric field at MP2-(FC)/6-311+G(d, p)level, including the equilibrium structure, electric dipole moment, total energy, the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO), energy gap, infrared spectrum. The results show that the C-Br bond length extends and the electric dipole moment increases with the increase of electric field intensity, while the total energy and energy gap E_G decreases with increasing the electric field intensity. The external electric field influences the vibration frequency and absorption intensity of infrared spectrum of CH₂BrCl molecule to varying degree. Discussing the molecule dissociation in the external electric field, the potential well decreases and gradually vanishes with the increase of the external electric field, which implies the bound ability of C-Br bond of CH₂BrCl molecule gradually degrade and the dissociation occurs.