Abstract: The urban inundation prevention effect of "sponge city" has not fully achieved the expected objectives. Basic research on the subject is relatively inadequate. To address this issue, this study examined the construction mode of urban inundation control systems in sponge cities, including the source control system (SCS), municipal drainage network system (DNS), and over standard stormwater storage and drainage system (OSS). The functions of the SCS, DNS, and OSS were quantified based on the local rain pattern in Tongzhou, Beijing. Under a 50-year rainfall event (339.85 mm/d), the design rainfalls of the SCS, DNS, and OSS were 34.00 mm, 130.70 mm, and 175.15 mm, respectively. Urban inundation control mechanisms were revealed by using a Gaussian function. The evaluation process of the urban inundation control function was transformed into a process of estimating the parameters of the Gaussian function. A method of optimizing the urban inundation control system is proposed for sponge city construction based on a cost-benefit analysis. The effectiveness of urban inundation control, the life cycle cost, and the covered area are adopted as decision indicators, while the maximization of cost-benefit per unit area under different scenarios is adopted as the objective function.