A rational exploitation policy for regional water resources is a fundamental condition for sustainable development of the regional economy and eco-environment. Faced with global change, rapid economic growth and population explosion, research on optimal decision making for a regional water resources system becomes much more important than ever before, especially in China today. In this paper, the plain area of Hanzhong Basin is used as a case study. Through systematic analysis of the regional water resources system, a system dynamics (SD) model is established. Based on the SD model, different exploitation scenarios are set up, and the optimal scenario and related exploitation policy are determined by multiscenario-multiobjective appraisal. The modelling and analysis methodology can be shared in other regions as well.