Annual average of river siIt carrying capacity for the water system of Dongting lake is about 40,593 million ton. The water area of Dongting lake is cutting down gradully because of serious deposit. Nowadays Dongting Iake, the largest freshwater lake of our country is taking th second place, that is at the back of Poyang lake in order of size. The trend of change for the river silt carrying capacity is rising steadily. In the seventies its amount is almost double that of fifties. The comprehensive harnessing of small watershed is a fundamental measure of controlling the river silt carrying capacity.