To assess the effects of cooling water from power plant on eutrophication in Xiangshan Bay Harbor,a dynamic model for nitrogen and phosphorus transport and transformation in mesocosm was established,in which 7 state variables(DIN,PO^3-₄-P,DON,DOP,phytoplankton,zooplankton and detritus)were included.Logically it had 5 modules—phytoplankton,zooplankton,dissolved inorganic nutrients,dissolved organic nutrient s and detritus.Not only the results showed that this model could simulate the variations of nitrogen and phosphorus nutrients in the pelagic ecosystem in mesocosm properly,based on the experiment data from one temperature section in Xiangshan Bay in October 2010,but also the conclusion was drawn that the effect of temperature elevation on Nitrogen and Phosphorus Transport and Transformation from simulation of mesocosms that belong to three different temperature sections.The results show that the cooling waters increased eutrophication of the receiving water in Xiangshan Bay.