Waterlogging is related to rainfall intensity as well as drainage network design. In previous studies, rainfall intensity was dominantly considered, while the design return period with the lowest total social investment of drainage networks was generally neglected. In this study, Guangkai Street in Tianjin in northern China was selected as a case study to determine the optimal design return period of drainage networks. According to the drainage networks for different design return periods, the depth of waterlogging was simulated based on the FloodArea model under the conditions of the rainfall exceeding the design return period. Furthermore, traffic losses due to waterlogging were determined by using the traffic loss model. When the sum of traffic losses and drainage network investment is smallest (i.e., the lowest total social investment), the corresponding return period is considered as the optimal design return period of drainage networks. By comparing the simulated depths of waterlogging and observations of 17 waterlogging monitoring points, we found that the FloodArea model has efficient simulation in most areas. Accordingly, the FloodArea model was used to simulate the depths of waterlogging with different return periods in Guangkai Street. The results show that the total social investment, including traffic losses and initial investment of drainage networks, is the lowest with the return period of the drainage networks in the selected area being designed as 5 years. This suggests that the design return period of the drainage networks in Guangkai Street should be upgraded to 5 years. The approach in this study is based on high-precision simulation (1 m GIS data) and actual waterlogging depth to ensure the accuracy of simulation. The optimal design return period is calculated in combination with traffic losses and initial investment of drainage networks, providing reference for the design of drainage networks in specific areas.