Using first principle calculations, we have investigated the adsorption of CO gas on various metal-decorated phosphorene. Almost all of the metals were considered to decorate phosphorene. By comparing binding energy (E b) and cohesive energy (E c), only 10 metals (Li, Na, K, Rb, Cs, Ca, Sr, Ba, Pd, and La) can stably decorate phosphorene and avoid clustering. CO adsorptions on these metal-decorated systems were calculated, and the mechanism of interaction between CO and metal atoms was analyzed in detail. E a shows a significant improvement after metal decoration, excerpt for Rb and Cs. The results imply that Li-, Na-, K-, Ca-, Sr-, Ba-, and La-decorated phosphorene could be used as CO elimination or reversible CO storage.