The variance of water quality was studied by adding different concent ration of nitrogen and phosphorus into the tested enclosure.The results show that:(1)There existed strong relationship between the hetero trophic bacteria abundance and the concentration of ni trogen and phosphorus, especially the phosphorus.(2)The nitrogen and phosphorus concentration and ratio of N to P significantly affected the algae abundance and biomass.The suitable N:P value for algae grow th was 10:1.(3)There existed signif icant relationship between the ni trogen and phosphorus removing capacity and the algae biomass and the N:P value.When the N:P value was 10:1, the algae grew well and the biomasses were increased most quickly.In this case, the nitrogen and phosphorus removing capacity was the highest.