Abstract: The water resources planning in the Jing-Jin-Tang (JJT)district is a multipurpose, large-scale and long-period complex problem which has profound effect on the development of the industry and the agriculture, and the people's life of the district. In this paper,a decision support system(DSS) prototype of JJT water resources plarming is established after analysing the problem in a system view. The DSS contains a user interface, a data base system, a model bank, a method bank, and a knowledge base system. In the model bank, there are system dynamic model and multi-purpose planning model, etc. In the method bank, there is a distance comparision method and a one-to-one comparision method, which is used for ranking the schemes. The knowledge base system contains some expert knowledge used for decision support. The logic and construction of the DSS of JJT water resources planning are emphatically stated in this paper.