Abstract: The principle and methods of hierarchical analysis for large-scale system are applied to solve the practical problems of optimal planning and operation for water supply in Beijing-Tianjin-Tangshan (JJT) area water resources system. A three-level hierarchical model for water resources planning and three-level hierarchical simulation model have been established. Simulation technique combined with optimization methods is presented. On the basis of simulation for 40 alternatives, among them 20 best alternatives are comprehensively assessed and are arranged in the order of priority by means of a developed JJT water resources decision support system and specific proposals are presented.