Based on a review of the problems and challenges of sponge city construction in China, the concept and methodology of an urban water system integrating urban rainstorm-runoff, water pollution control, and an urban ecological greenbelt with wetland and municipal construction(drainage and sewage)are proposed. Based on hydrological theories, the concept of the control rate of total annual runoff, which is the most critical and difficult-to-quantify factor in the construction of a sponge city, is analyzed. It is pointed out that the currently calculated control rate of total annual runoff is actually the control rate of total annual precipitation. Hence, it is necessary to establish an internal relation with the gain factor of the response of the hydrological system, i. e. , the runoff coefficient. It also needs to be noted that the runoff coefficient is not a constant, but the time-varying nonlinearity of the combination of soil moisture, precipitation intensity, and the underlying surface. Additionally, the relationship between low impact development(LID)during sponge city construction and the improved control rate of total annual runoff are analyzed, in order to examine the conditions and risks of sea views in cities. Finally, it is suggested that the runoff coefficient nonlinearity, the differences in storage capacity between natural conditions and the conditions after urbanization, river and lake water system storage and land evapotranspiration, basin sponge regulation and control, and risk management should be strengthened on the hydrological basis of sponge city construction and planning. Some suggestions for future sponge city construction in China are put forward.