Abstract: To explore four quite underwater plants in the high concentration of nitrogen and phosphorus stress tolerance ability of the polluted water,artificial simulated water conditions on the dynamic change of nitrogen and phosphorus,nitrogen and phosphorus in the outdoor tolerance pot experiment,through the study of plant antioxidant enzyme defense system main enzymology indexes superoxide dismutase（SOD）and catalase（CAT）activity and malondialdehyde（MDA）content,this paper determines the tolerance range of nitrogen and phosphorus of four emergent plants. The results show that with the increase in nitrogen and phosphorus concentration,the activities of SOD and CAT in the four plants increased first and then decreased,while the content of MDA gradually increased and began to decline after exceeding the plant tolerance capacity. The final conclusion is that the tolerance range of the plants to ammonia nitrogen is as follows:calamus and cattail:20～400 mg/L,canna and reed:20～500 mg/L,phosphorus tolerance range was as follows:calamus:2～200 mg/L,canna,reed and cattail:2～300 mg/L.