Abstract: Under the background of systematically promoting the construction of sponge city in the whole Suqian City of Jiangsu Province, in order to give full play to the role of spongy bodies such as river and lake systems, Suqian City has carried out a study on the connection between different flood control and drainage systems, and conducted a combination analysis of regional rainstorm and outer river level. The old urban area of Suqian City was selected as the research area. The GH Copula function with the highest fitting accuracy was selected for the combination analysis of regional rainstorm and outer river level encounter in Suqian City, and the outer river level with the greatest probability of encounter under different design rainstorm conditions was calculated. The results show that the maximum probability of a 2-year design rainstorm encountering a river level of 18.6～18.7 m, the maximum probability of a 3-year design rainstorm encountering a river level of 18.9～19.0 m, and the maximum probability of a 5-year design rainstorm encountering a river level of 19.0～19.1 m. The research results can help realize the effective connection of urban drainage and flood control, which is of great significance to improve the overall optimization and collaborative development of urban water systems, and provides scientific reference for the construction of systematic sponge city in Suqian City.