In view of the existing problems of water resources utilization in Beijing, this paper simulated the water supply and demand for this city from 2012 to 2030 by establishing a system dynamics model. The results showed: the water supply and demand contradiction in Beijing is very prominent, with the water shortages in 2020 and 2030 of 1.095 and 0.844 billion m3 respectively and the corresponding water shortage rates of 31.33% and 20.75%. This contradiction has been greatly improved under the scenario of second time water supply and demand balance analysis, with water surplus in 2020 and 2030 of 0.236 and 0.443 billion m3 respectively. It is unacceptable for Beijing, as this surplus of water was achieved by emphasizing the protection of resources and environment and ignoring the rapid economic development. In order to ensure the rapid development of social economy and maintain water supply and demand balance and sustainable development, Beijing also needs more efforts to enhance the people's awareness to protect water resources and save water. Only in this way can the long-term balance of water supply and demand be achieved in Beijing.