We studied the distribution characteristics of dissolved inorganic nitrogen(DIN) and dissolved inorganic phosphorus(DIP), as well as their affecting factors in water of the Xinghua Bay based on the monitoring data of water quality from March to December, 2007.Besides,we assessed the nutrient level in the bay using organic pollution index and eutrophication index.The results showed that DIN and DIP were major pollutants resulting in eutrophication in the bay,which were mainly affected by runoff discharge and marine phytoplankton growth.In spring and summer seasons,phytoplankton grew and reproduced rapidly,and the rainfall increased,eventually leading to an increase of DIP and DIN concentrations.In autumn,water temperature decreased;phytoplankton grew and reproduced slowly;DIP and DIN concentrations also increased.Eutrophication became more and more serious in the Xinghua Bay.The eutrophication index in 2007 was 5.7 times higher than that in 2000,representing by the increased indexes of DIN and DIP.