The shortage of water resources restricts Beijings global city position in the 21th Century. With the assistance of the definition of a quasi-nature process of water dynamics by a metro-population body, this paper presents a construct chain consisting of water-genesis structure, water conservation structure and water-consumption structure, which enabling the authors to argue that the dynamic disequilibrium of the chain is caused by the metro-sized urbanization. With the analysis of Beijings water supply-demand cycle over half a century, the authors indicate that: The marginal reservation of water resources is roughly equal to variation of the precipitation, and both decrease relative to their long-term levels; the consumption in 2001~2012 was up to a higher level than the annual amount the local could supplied, a dynamic disequilibrium of water ecological system. Through regressions, the authors, then, reveals that there exists a correlation between the climate change and human activities, and points out the behavioral pattern of metro population body is a contribution factor of the disequilibrium. In the end, the authors raises up some advice for reform and projects inversing the disequilibrium.