In order to break the “black model” of water dissipation in urban area, statistical analysis, experimental observations and case studies methods were used to analyze the urban water dissipation phenomenon and to explore its mechanism. Results showed that cities belong to the high water dissipation area, and the intensity of water dissipation is not only related to meteorological factors such as precipitation and temperature, but also closely related to human activities. Taking Beijing City as an example, this paper established a calculation model of urban water dissipation, and calculated the spatial distribution value of water dissipation in Beijing in 2014 based on land use data. Considering the water dissipation of human water use activity, the water dissipation in urban areas was significantly higher than that of suburbs and the evapotranspiration of natural underlying surfaces.