The Three Gorges Dam is the largest water conservancy project in Yangtze Vally. After constructing Three Gorges Dam, the eco-system of whole Yangtze Vally is going to be changed. The eco-environment, bio-community, and fishery resources around the Yangtze Mouth and its nearby sea area are going to be affected because of the adjustment of Yangtze runoff. Thus, the changing of the Condifion of hydrology, hydro-chemistry and sedimentary environment will change, the composition and distributed pattern of bio-community which will cause the decreasing fo the biobait and the fishery resources to a certain extent.