The article set up model of phosphorus-algae on the basis of establishing total phosphorus model in early period. From the start of inorganic salts represented by orthophosphate and organophosphorus represented by algal biomass, it analyses at high water level stages, kinds of form transformation and cycle mechanism of accumulated phosphorus due to impounding stage in order to explain the source of the phosphorus which is consumed by the outbreak of water bloom at the end of winter from fixed quantity and fixed nature two parts. The research shows that the total phosphorus of phosphorus pool in the three phases of impounding stage, stable stage and algae bloom stages at high water level in Lake Gaoyang is totally different. Water-level-fluctuating zone with phosphorus release is a major source of solubility reactive phosphorus at high water level in Lake Gaoyang (72.69% of the total input flux), which is related to the area of water-level-fluctuating zone and the phosphorus exchange rate in the soil and water interface of water-level-fluctuating zone. More flooded area, the higher exchange rate of phosphorus, more phosphorus release, the greater contribution of the phosphorus cycle. And the maximum synthetic ratio of phosphorus-algae was only 14.4%. However, the amount of utilized phosphorus at algal bloom stage was small.