[Objective] As a key national urban agglomeration in the upper Yangtze River Basin，the Chengdu-Chongqing urban agglomeration features pronounced topographic contrasts，rapid urban expansion，and increasingly frequent extreme rainfall events，resulting in highly complex and multi-source flood impacts. [Methods] This study integrates passive microwave remote sensing precipitation data，multi-source rainfall datasets，land-use data，nighttime light imagery，and population data to construct a comprehensive indicator system comprising precipitation，waterlogging，impervious surface ratio，and development level. From the perspectives of hazard factors，rainfall triggering mechanisms，surface water accumulation processes，and urban expansion patterns，the spatiotemporal evolution of flood vulnerability in the Chengdu-Chongqing urban agglomeration from 1995 to 2020 is systematically analyzed. [Results] （1） Flood vulnerability exhibited a staged increasing trend during 1995-2020，with significant peak years in 2000 and 2020；（2） urban construction land expanded rapidly over the past three decades （an increase of 4，232 km²），mainly through the conversion of cropland，which significantly altered surface characteristics and intensified runoff concentration；（3） extreme rainfall and surface waterlogging intensity increased markedly in 2000 and 2020，forming a spatial pattern of “strong triggering in southwestern mountainous areas and easy waterlogging in eastern lowlands”；（4） flood vulnerability shows a non-linear relationship with urban development level—vulnerability decreased in Chongqing due to favorable terrain and enhanced flood control infrastructure，whereas it increased in Chengdu and surrounding plain cities due to rapid expansion and increased impervious surfaces；（5） approximately 42% of newly developed urban construction areas experienced waterlogging in 2020，with some plain cities exceeding 80%，indicating insufficient resilience in rapidly expanding areas. [Conclusions] Urban flood vulnerability is not solely determined by the level of development； rather，it is jointly influenced by topographical conditions，patterns of urban expansion，and engineering regulation capabilities. The Chengdu-Chongqing urban agglomeration faces compound flood processes involving both basin-wide floods and urban waterlogging. Therefore，measures should be taken to improve flood control and drainage standards，optimize urban spatial structures，strengthen sponge city initiatives，and enhance coordinated regulation between upstream and downstream areas within the urban agglomeration.These findings provide scientific support for flood disaster mitigation，vulnerability reduction，and resilient urban development in the Chengdu-Chongqing urban agglomeration.