The nationwide Sponge City Construction (SCC) program was launched by the Chinese government in 2014. There is a lack of an integrated model system to assist the efforts throughout all the SCC phases, including planning, design, construction, evaluation and maintenance stages. In this study, an integrated stormwater system named Uwater was developed based on a Geographic Information System (GIS) platform, in which a comprehensive open-source urban stormwater runoff model called Storm Water Management Model (SWMM) was embedded. The platform utilized the spatial data management tools in GIS to extract the discrete spatial information such as land use and vegetation cover condition to obtain the composite hydrologic parameters required in the SWMM simulations. The system also fully uses the visualization capabilities of GIS to assist visual design of the Low Impact Development (LID) facilities and Capital Improvement Projects frequently used in the SCC programs. Furthermore, it could be used to assess the drainage capacity of the stormwater system and the corresponding inundation limits for further optimization of the design plans. Finally, a study case using the platform was conducted to test and verify the reliability and applicability of the Uwater system. Results show that the Uwater platform has great strengths and potential to assist the whole life cycle in the SCC program.