We have studied the adsorption and decomposition of several poisonous gases (H2S, HCN and NH3) on metal (Li, Mg, Al, Ni and Pt) absorbed phosphorene by means of density functional theory. The results indicate Pt-decorated phosphorene has the strongest adsorption capacity for H2S due to the maximum adsorption energy of - 1.101 eV in all possible structures of H2S on metal-decorated phosphorene. HCN and NH3 could be effectively captured by Al and Ni-decorated phosphorene with large adsorption energies of -2.166 and -1.284 eV, respectively. Considering the low price and more friendly environment of Al light metal, the strong adsorption ability of HCN shows that Al-decorated phosphorene is very promising to remove toxic gases. The energy barrier of the first dehydrogenation for poisonous gases on metal decorated phosphorene is relatively low, which shows the dissociation process is favorable, while the second dehydrogenation has a higher energy barrier, suggesting the decomposition process is difficult to occur.