This paper,being concerned in the sewage discharge of the point pollution sources in Donghu Lake, selects three principal ditches, and mainly deals with the changes of sewage flow, concentration and load of nitrition materials(nitrogen and phosphorus).Studies of development of N and P contents in waste water in ten years (1982-1992),have also been made.The results of studies indicate: (1) the input of external nitrition materials (N, P), especially in the surrounding residant's domestic demand,has greatly contributed to the eutrophication of Donghu Lake. (2) the input of total nitrogen and total phosphorus has increased greatly, and the latter's ratio between 1982 and 1992 reaches to 1:2.09. (3) the main pollutants are NH₄⁺-N and soluable phosphorus, which are related to the use of great amount of phosphorus-containing synthetic detergents.So, one of the most practical means of controlling the eutrophication of Donghu Lake is to reduce external nutrient input.