Abstract:According to investigations in the Shuangdao Bay,Weihai,in June2015,including DIN,PO4-P and COD, nutrients characteristics in concentration and restrictive analysis were studied, and the eutrophication degree of the Shuangdao Bay was assessed by single factor index, eutrophication index and organic pollution comprehensive index. The results showed that NO3-N was the chief form of DIN,and DIN was the principal contamination parameter for water quality of the Shuangdao Bay. The mean concentrations of DIN, PO4-P and COD were 164.99μg/L, 4.51μg/L and 0.93mg/L,respectively.Except for concentrations of DIN in some monitoring stations, the concentrations of DIN, PO4-P and COD in all the reststations attained the gradeⅠStandard of Seawater Quality.In general the horizontal distribution of nutrients and COD of Shuangdao Bay tended to be higher in the south than the north, and higher in the inside than the outside. The mean ratio of N: P of Shuangdao bay is 83.04, and the structure of nutrients is characterized by phosphorus-limitation in the Shuangdao bay. Comparing with historical data, the imbalance of N: P ratio is getting more serious year by year. The average rate of eutrophication index in Shuangdao bay is 0.16, and the organic pollution comprehensive indices of twelve investigations range from -0.62~1.02. The results of organic pollution comprehensive index are more objective than those of the eutrophication index.