Abstract: To realize efficient calculation of waterlogging risk in mountainous cities without pipe survey data, this paper takes a drainage subarea in Nan’an District of Chongqing City as the study area, and the panoramic static API function provided by Baidu Maps open platform is used to identify and locate the rainwater wells. The equivalent drainage method of rainwater wells is used to establish a storm flood model based on LISFLOOD-FP, and the ideal calculation case and historical rainfalls are used to verify the model, and the waterlogging characteristics such as the flood area, flood volume, and the distribution of waterlogging under different rainfall scenarios are simulated and analyzed in the study area. The results show that in the area without pipe survey data, the rainwater wells in the area can be effectively determined by using the panoramic static API function of Baidu Maps open platform. The growth of flood volume and flood area shows a synergistic effect, and the larger the return period, the greater the flood area and flood volume at the same time. The time when the growth rate of flood volume is the fastest is basically consistent with the time when the flood area reaches its peak, both of which lag behind the rain peak time. During the period of decreasing flood area, the flood volume is still increasing, indicating that steep slope sections may face high flood flow rates and have potential disaster risks for vulnerable groups. For mountainous cities with fluctuating terrain, bridge deck runoff may exacerbate local waterlogging levels and should be given attention. Based on the LISFLOOD-FP model, the full hydrodynamic surface runoff simulation is carried out by using the equivalent drainage method of rainwater wells and the direct rainfall method. Even when running on an ordinary personal computer, it still has high computational efficiency and can achieve efficient calculation of rainwater and flood in a large area and identification of waterlogging prone points. The proposed simulation calculation method can provide technical reference for efficient assessment of waterlogging risk in mountainous urban areas without pipe survey data, and also provide a reference for the use of the LISFLOOD-FP model in China.