Because phosphorus is one of the essential elements to Blue-green algae, a lot of researches on nutrient physiology of phosphorus have been made and most of them are effects of ambient phosphorus on cells. In this paper Anabaena variabilis was used for the study of the relationships among the phosphorus concentrations in medium, intracellular phosphorus, and physiologic status of cell. Moreover, several phosphorus fertilizers' effects on the growth and N. fixation of A. variabilis were also observed. In a comparative study in batch cultures, the phosphorus concentrations in medium for growth of A. variabilis ranged from 1 to 10 ppm. Nitrogenase activity and nitrogen content of cells which grown in 10 ppm P were the highest. Phosphate concentrations in the culture media below or excess about 10 ppm resulted in a rise in the cellular C/N. It was found that external phosphate concentration influenced the amounts of phosphorus concentration compounds in the cells. The external phosphate concentrations caused a higher phosphatase activities showed an inverse relationship with external phosphate or total cellular phosphorus levels. Phosphorus-stored in cells that was first used was almost phosphate in cold TCA extract and orthophosphate in the hot TCA extract when cells were transfered from phosphorus sufficient culture condition to a phosphorus-free medium. However, within 5 days of phosphorus starvation, the algal biomass (dry weight) still incr eased with the decreasing of cellular phosphorus. Adding phosphate to the phosphorus-starved cells led to increase in all cellular phosphorus fractions and their ability to reduce acetylene to ethylene. The rate of N_2 fixation increased obviously. Within uptake four hours, the rate of N_2 fixation recovered to normal. Alkline phosphatase activity didn't immediately fell with phosphate addtion. Results indicated that the alkaline phosphatase activity in A. variabilis may be controlled by some intracellal phosphorus pool rather than ambient phosphate. We have compared available effect of several phosphorus fertilizers which were used is rice paddy. It was found that CaMgP fertilizer had the best off-ectiveness for A. variabilis in the rate of N_2 fixation and growth rate.