A long-running SF6 insulating gas decomposes without being detected in time would cause incalculable consequences, therefore, real-time monitoring towards SF6 status is of practical significance. Currently, the gas-sensitive properties of two-dimensional materials are the focus and hotspot of gas sensor research, however, in practical situations, material preparation and device fabrication will inevitably bring about defects. Therefore, the effects of sulfuric vacancy (SV) in molybdenum disulphide are proposed and explored, and a comparative study of gas-sensitive properties (pristine MoS2 vs SV- MoS2) is carried out using density functional theory based on the first principles. Constructing typical adsorption models for SF6 decomposition components on monolayer, together with analyzing the optimum adsorption structures, adsorption energy, density of states, molecular orbitals, electrical conductivity and co-adsorption behaviors. The results show that the SV brings a defective state to MoS2 monolayer, which contributes to an overall increase in the adsorption energy for the decomposition components (the increase > 0.15 eV), making the undifferentiated adsorption effect selective for SO2F2. The physical interaction between the decomposition products and SV-MoS2 monolayer is more favorable for desorption. These results indicate it is appropriate for detecting SF6 status in high-voltage insulation environments, with pointers to practical applications for two-dimensional materials.