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.