This work reports a novel strategy to improve phosphorus resistance of a model Pd catalyst on alumina using CePO4 as an additive, and the mechanism of phosphorus poisoning over the catalyst for methane removal under operational conditions was systematically investigated. The results demonstrated that phosphorus poisoning at 800 degrees C caused both harsh physical and chemical modifications in the Pd catalyst without the CePO4 additive; that is, the conversion of support aluminum oxide into a multilayer cristobalite-type aluminum phosphate led to considerable change of the catalyst texture and structure and remarkable blocking of Pd-active sites. However, CePO4 acting as a barrier layer can effectively suppress the formation of the inactive aluminum phosphate and also hinder the accumulation of Pd nanoparticles. Owing to the nearly maintaining of Pd-active sites, the modified catalyst shows much better performance (i.e., a wider A window and a lower light-off temperature) with respect to resistance to phosphorus poisoning and thereby retains its activity of methane conversion.