Since the relation between the pollution source and the receiving water body was established by the water quality model, recently water quality model has become one of the most important tools for watershed environment management planning. As a planning tool, water quality model should be composed on the basis of full understanding of the complex physical, chemical, biological processes of water systems, able to provide realtime and visible information on watershed environment, and easy to apply for practical purpose. Interactive computer simulation techniques are expected suitable to the composition of water quality model with above functions. In this study a Windows-based simulator of the water environment of Yangong watershed in combination with Geographic Information System (GIS) has been developed. The simulator can quickly andinteractively provide both digital and graphical information necessary for controlling water pollution of Yangong river and watershed management.