The adsorption and gas sensing properties of black arsenene (B-As) regarding sulfur hexafluoride (SF6) and its six decompositions (SOF2, SO2F2, SO2, H2S, HF, and CF4) are investigated using density functional theory combined with the nonequilibrium Green's function. The sensitivity of B-As is evaluated by considering the most stable adsorption configuration, adsorption energy, work function, recovery time, local density of states, and charge transfer between the gas molecules and B-As. It is demonstrated that B-As is more sensitive to the SO2 molecule than to the other decompositions. Additionally, the adsorption strength can be manipulated by controlling the external electric field (E-field). The application of tensile biaxial strain results in more isotropic electrical conductance of B-As, and it can also effectively enhance the response toward SO2. For example, under a 1% equibiaxial tensile strain, a 132% response can be obtained along the zigzag direction. This work suggests the promising prospects of B-As-based gas sensors for detecting SO2 among SF6 decompositions.