Abstract:In this paper, the water supply and demand situation in Nanyang City, Which is the location of the head of the Middle Route Project of South-to-North Water Diversion, was simulated using system dynamics model. Based on the analysis of the factors affecting the balance of water supply and demand, three social and economic development programs of Nanyang City, that is, “traditional development mode”, “emphasized economic growth development mode” and “economic and environmental coordination development mode” were assumed. Meanwhile, future water resources supply and demand balance were analyzed. The results showed that under the “traditional development mode”, Nanyang City would face severe water shortages in the future years; under the “emphasized economic growth development mode”, water shortages in Nanyang City would be further intensified; under the “economic and environmental coordination development mode”, there would be a minimum conflict between water supply and demand. Therefore, in order to solve the contradiction between water supply and demand and ensure water supply security of South to North Water Diversion Project, the economic development mode should be changed as soon as possible and some effective measures, such as relying on water-saving investment, technological progress, water resources management and other means, should be taken to improve the utilization of water resources. Only in this way can we fundamentally reduce the amount of water resources, maintain water supply and demand balance water resources and can the social economy develop continuously and healthily.