Abstract: This paper presents the quantitative assessment and prediction results of the nutrient states in the subtropic/tropic waters. By using the method of relative weighed nutrient status index, the nutrient states of H Reservoir were continuonsly and numerically assessed. it revealed the steps of nutrient development and processes of eutrophication, which overcame the limitations and overlaps of nutrient status assessments for lakes and reservoirs by using fixed parameters. Based on the responding relation between lake external force functions(mainly the concentrations or loadings of external nutrient salts)and the research result of international cooperative organization of OECD, mathematical models of phosphorus concentrations of H Reservoir responding to nutrient salts inflow loadings and control standards are put forward and the results are identical with reality. Assessing methods and predicting models raised in this paper could also be applied to other lakes and reservoirs in the subtropics/tropics.