Abstract: We investigated the spatio-temporal distribution characteristics and eutrophication of nutrients in Daya Bay in April and May 2009, May and June 2010, February 2012, as well as January and February 2015. Generally speaking, the contents of DIN and PO₄-P increased first and then decreased. The spatio-temporal distribution of DIN and PO₄-P was affected by terrestrial pollution, marine aquaculture, etc.. The nutrient concentration decreased from coastal area to open sea. The evaluation of potential eutrophication indicates that the seawater in Daya Bay experienced a process from poor nutrition to moderate nutrition and then to poor nutrition. The seawater in the functional areas of Class I had been always in a state of poor nutrition. The average N/P ratio was lower than the Redfield value (16) in the monitoring period.