Abstract: To assess the risk of urban flood inundation due to inadequate drainage, this paper proposes an urban inundation risk assessment method based on a coupled surface-pipe-river system. An urban runoff and flood inundation risk assessment model was established for Changzhou urban runoff and flood inundation experimental site and conducts flood risk simulations under various designed rainfall scenarios. Results indicate that manhole overflows predominantly occur in the downstream section of the pipe, influenced by the pipe burial depth and drainage capacity. As the return period (P) increases, the proportion of fullness pipe increases from an average of 72.46% to 82.27%, and the proportion of overflow manhole increases from 1.95% to 4.11%. Although most areas did not experience manhole overflow, multiple urban flood sites still occurred within the study area, with the risk area ratio increasing from 4.31% (P =5 a) to 6.19% (P =50 a). The urban flood inundation risk assessment method based on a coupled surface-pipe-river system can more comprehensively reflect the urban inundation risks, offering new insights for assessing urban flood inundation risks.