The Liyangkeng watershed features mountainous terrain in the east and the north, adjacent to the Oujiang River and the Haoxi River, with a topography sloping from high in the north to low in the south. The river traverses the main urban area of Lishui City. Due to its unique topography, it is a region prone to frequent flooding. Addressing the spatial distribution characteristics of the watershed – a natural upper basin and a residential lower basin – and the scenario of external flooding and internal waterlogging, the STFS-Urban (Spatio-temporal flood simulation model for urban，STFS-Urban） was selected to conduct comprehensive coupled modeling and simulation of urban flooding in this watershed, integrating "surface-pipe-river" interactions. Based on the flood scenario simulation results from the STFS-Urban model, combined with natural and social data from Lishui City, the potential flood risk in the urban area of the Liyangkeng watershed was assessed. A comprehensive evaluation index system for urban flood vulnerability within the watershed was constructed from three aspects: exposure, sensitivity, and adaptability. The degree of urban vulnerability under flood scenarios was used to reflect the risk level. The results indicate that the STFS-Urban model demonstrates good accuracy in simulation. As the return period increases, high-risk areas increase significantly, concentrating near river confluences. This provides key reference points for urban flood control and drainage planning.