Phosphorene is a promising candidate for gas sensing materials. This letter describes our study of the adsorption of SF 6 and SF 6 decomposition gases (SO 2 and H 2 S) on phosphorene. We used first principles calculations to explore phosphorene's potential applications as gas sensor to diagnose the state of online gas insulated switchgear (GIS). The calculation results showed that only the adsorption of SO 2 induced a moderate adsorption energy and apparent charge transfer. We further investigated the current-voltage (I-V) relationships before and after gas absorption through the non-equilibrium Green's function method. It was found that only SO 2 induced a dramatic change in the I-V relationships. Therefore, phosphorene appears to be a promising candidate for highly sensitive and selective SF 6 decomposition gas sensors for online GIS diagnosis.