Abstract: In recent years, Lake Erhai is experiencing a transition from the mesotrophic to eutrophic condition and cya-nobacterial blooms have a rapid increase in the lake. In this study, the dominant species from the bloom of Lake Erhai, Anabaena spiroides, was isolated and purified. The growth and physiological characteristics of an Anabaena spiroides strain under different environmental conditions were studied to evaluate the influence of environmental factors on Anabaena bloom formation, and the growth was determined by cell biomass and relative growth rate. The results showed that the Anabaena the contents of nitrogen 1.5mmol/L and phosphorus 12mol/L. The activities of nitrate reductase (NR) and alkaline phophatase (APA), which indicate metabolism of nitrogen and phosphorus, were measured with different concentrations of nitrogen and phosphorus. NR activity of the Anabaena spiroicles strain increased with the raising of nitrogen concentration when nitrogen supply level was low (0-0.36 mmol/L). But the activity of NR was related to the growth under the condi-tion of rich nitrogen supply (0.36-6 mmol/L), i.e. the better strain's growth, the higher NR activity. APA activity of the Anabaena spiroides strain largely depended on the concentration of phosphorus. APA activity was lower with more phos-phorus supply. And Nitrogen did not play an important role in the activity change of APA when phosphorus supply was rich. In addition, it was observed that the Anabaena spiroides strain could grow with low concentration of nitrogen or phos-phorus. This may be related to special regulatory mechanism of nitrogen fixing and phosphorus utilizing of Anabaena.