The process of water purification was studied using immobilized nitrogen cycling bacteria, including ammonibacteria,nitrosobacteria, nitrifying bacteria and denitrifying bacteria, which applied and screened for natural water of Lake Jinshan. The resultshowed that the water quality was improved obviously after running a period of time. Concentrations of NH₄⁺ -N, NO₂^--N, NO₃^- -Nand TN declined. NH₄⁺-N concentration had reached national Ⅰ class of water quality index. TN concentration had reached Ⅱclass.The N₂O flux of Lake Jinshan increased during three months from April to June, which were 23.51μg/(m²·h), 29.52μg/(m²·h) and59.10μg/(m ²·h) respectively. The experiment has proved that the techniques of immobilized nitrogen cycling bacteria could purify theurban lakes significantly.