Abstract: This thesis started from equations of discharge and heat balance on earth surface, and discussed changes of the whole hydrothermal condition in the reservoir area after the Three Gorge Project being built through analysis of a series of variables. The preliminary estimates show that the surface radiation balance in the area along the reservoir will have a increase of 4.2%-6.7%, namely 8.0-12.6?10³J/cm²·a, and the surface evaporation capality will also rise by 2.2%-3.9%,namely 12-21 mm/a. But the surface runoff in the reservoir area tend to descend about 8%-10%, mean 45-55 mm/a. In addition, the latent heat exchange and the turbulent heat exchange between earth surface and atmosphere will increase in different extents. The above mentioned conclusion has momentous significance to understand eco-environmental evolution in reservoir area.