Total nitrogen, total phosphorus, biomass in three eutrophic waters were investigated in the rapid-growth season of phytoplankton (July～October). Chloromonas rosae was cultivated in water samples from three eutrophic waters and diluted water samples from Lake Donghu to determine the effect of N and P concentrations on growth rate. The relationship between biomass and N and P concentrations, analyzed by regression, showed that phosphorus was the limiting factor for algae growth in eutrophic water. The relationship between growth rate and P concentration can be described with the regression equation y=0.0806lnx+0.4658, (Ｒ^２=0.889). Growth rate increased linearly with the increase of P concentration when it was below 0.05 mg/L, Growth rate was less increased when the P concentration was above 0.05 mg/L, and was almost unaffected when the P concentration exceeded 0.2mg/L. The P concentration corresponding to growth rate “0" (deduced from a regression equation) was 0.003mg/L, close to the minimal P concentration of poor nutrient lakes. This indicated that the regression equation was representative. The average values for planktic cellular N and P in the three eutrophic waters were respectively 53% and 85%.To evaluate the levels of eutrophy, N and P both in the water and in the plants must be considered. The biomass of phytoplankton is controlled by concentrations of both dissolved and cellular N and P. The following linear regression equations describe the relationship between biomass and N: y=10.687x－7.8304, (Ｒ^２=0.950), biomass and P, y=122.11x-12.069, (Ｒ^２=0.991) They exemplify the absolute and relative aspects of growth-limiting factors with Redfield values. We conclude that the only way to prevent eutrophication is to maintain a balance between the input and output of nutrients and to remove excessive dissolved N and P in the water