Coastal　cities　globally　face　escalating　flood　events　under　climate　change　and　rapid　urbanization,　threatening　sustainable　development.　While　urbanization　amplifies　flood　vulnerability　(FV),　inconsistent　relationships　between　urban　expansion　patterns　(UEPs)　and　FV　persist.　To　address　this　gap,　this　study　resolves　UEP-multidimensional　FV　relationships　while　examining　inter-city　developmental　disparities　through　an　integrated　assessment　of　China＇s　Min　Delta　Urban　Agglomeration　(1990–2020),　combining　Landscape　Expansion　Index　with　entropy-weighted　multidimensional　FV　metrics　validated　by　Geographically　Weighted　Regression　and　correlation　comparisons.　Results　reveal　regional　expansion　peaked　during　2000–2010　before　declining,　except　Zhangzhou,　where　delayed　urbanization　sustained　growth.　Edge　expansion　(EE)　dominated,　infilling　expansion　(IE)　intensified,　and　leapfrog　expansion　(LE)　remained　minimal.　Due　to　persistent　urban　expansion,　natural　vulnerability　(NV)　increased　inland-to-coastal　and　intensified　continuously,　and　social　vulnerability　(SV)　shifted　toward　moderate　dominance　as　regional　integration　policies　balanced　regional　development,　while　comprehensive　vulnerability　(CV)　underwent　polarization-concentration-repolarization　dynamics　under　dual　natural-social　influences.　UEPs　exhibited　significant　positive　FV　correlations,　strongest　for　EE　(R　=　0.536,　p　©　2025　Elsevier　Ltd