An aquatic plant bed system was used to study the effects of different nitrogen forms (nitrate, nitrite, and ammonium) on nutrient removal by Iris pseudoacoru. Meanwhile, the plant growth, solution chlorophyll-a concentration TN and TP uptaken by Iris pseudoacorus, the distribution of nitrogen cycle bacteria and flux of nitrous oxide were analyzed. The results showed that Iris pseudoacorus has prior selectivity on different nitrogen forms and has worse removal effect on ammonium N and nitrogen N. From the view of uptake of N and P by the plant, nitrate N>nitrite N>ammonium N; from the view of amount of nitrogen cycle bacteria and release of N2O, nitrate N > ammonium N > nitrite N. The uptake of nutrients increased with the increase of concentration of nitrogen in a certain range. When the concentration is too high (80 mg/L), the growth of plant is inhibited.The wet weight of plant is obviously decreased in solution of high concentration.In conclusion, Iris pseudoacorus is more suitable to be used in the water body polluted with nitrate.