This paper introduced the idea of environmental carrying capacity (ECC) to the planning of watershed’s environmental-economic optimization. And a case study in Lake Fuxianhu is utilized from year 2008 to 2028. The results are: based on the water environment carrying capacity of lakes, with the adjustment of industrial internal structure, distribution and development speed of three major industries, the water quality of the basin will be I class. This adjustment will not only keep a rapid development of economy, but also can make sure the improvement of Lake Fuxianhu Basin environment. Thus, the development of society and environment will be coordinated. The application of water environment carrying capacity of lakes to instruct the scale of social development is very significant to the sustainable development among economy, society and environment.