Abstract Urban flooding is caused by multiple factors, which seriously restricts the sustainable development of society. Understanding the driving factors of urban flooding is pivotal to alleviating flood disasters. Although the effects of various factors on urban flooding have been extensively evaluated, few studies consider both interregional flood connection and interactions between driving factors. In this study, driving factors of urban flooding were analyzed based on the water tracer method and the optimal parameters-based geographical detector (OPGD). An urban flood simulation model coupled with the water tracer method was constructed to simulate flooding. Furthermore, interregional flood volume connection was analyzed based on simulation results. Subsequently, driving force of urban flooding factors and interactions between them were quantified using the OPGD model. Taking Haidian Island in Hainan Province, China as an example, the coupled model simulation results show that sub-catchment H6 is the region experiencing the most severe flooding and sub-catchment H9 contributes the most to overall flooding in the study area. The results of subsequent driving effect analysis show that elevation is the factor with the maximum single-factor driving force (0.772) and elevation ∩ percentage of building area is the pair of factors with the maximum two-factor driving force (0.968). In addition, the interactions between driving factors have bivariable or nonlinear enhancement effects. The interactions between two factors strengthen the influence of each factor on urban flooding. This study contributes to understanding the cause of urban flooding and provides a reference for urban flood risk mitigation.