Sulfuryl fluoride( SO2F2) is a powerful greenhouse gas that threatens human health. Now, it is essential to study the dissociation mechanism under external electric fields. Based on the density functional theory( DFT), the stepwise and concerted dissociation properties of SO2F2 are studied under external electric fields, including depolo moment, bond length, the total energy, orbital energy level distribution, and the infrared spectrum. Result description: when the external electric field increases the bond length of 1S-4F&1S-5F becomes longer and tends to break, the total energy decline; The HOMO-LUMO energy gaps become decline. Infrared spectroscopy showed the vibration frequency of 1S-4F&1S-5F bond str vibration frequency becomes lower as the electric field increases and significant redshift. TD-DFT (time-dependent density functional theory) is used to describe the ultraviolet-visible absorption spectra; Additionally, the potential energy curve along with the S-F bond under electric fields was calculated, it indicated the stepwise dissociation occur when F=0.08 a.u. in 1S-4F and F=0.06 a.u. in 1S-5F; The corrected dissociation occurs when increases F=0.1 a.u. The consequence provides an important reference for environmental protection and electric field degradation of SO2F2.