Using the first-principles calculation based on density functional theory (DFT), we systematically studied the adsorption of sulfur-based gas molecules (H2S, SO2, SO3) on various metal-decorated phosphorenes. To avoid the formation of metal clusters on the surface of phosphorene, eleven metals (Li, Na, K, Rb, Cs, Ca, Sr, Ba, Ni, La, Tl) with bulk cohesive energy less than the binding energy on the phosphorene are considered. Except for H2S on Tl-decorated phosphorene, all metal decorations can improve the adsorption strength of phosphorene to sulfur-based gas molecules, and Eads(H2S) < Eads(SO2) < Eads(SO3) for the same metal decoration case. In addition, some metal-decorated phosphorene systems exhibit interesting magnetic and electrical changes after sulfur-based gas molecule adsorptions, indicating that these metal-decorated phosphorene systems are promising to be used for the detection and removal of sulfur-based gas molecules.