Floods represent one of the most destructive natural hazards worldwide, threatening human lives, infrastructure, economic progress, and ecological systems. The impacts of floods have been exacerbated by global climate change and increasing anthropogenic activities, particularly in hydrologically sensitive and ecologically vulnerable regions such as the middle reaches of the Yellow River Basin in China. In this context, traditional flood risk assessments—often limited to either human or ecological perspectives—fall short in capturing the multifaceted dynamics of modern flood risk. To address this gap, this study develops a comprehensive flood risk assessment framework that explicitly couples human society and ecosystems as disaster-bearing bodies. The assessment employs a multivariate joint distribution model based on the Copula function to estimate flood occurrence probabilities by integrating peak discharge and flood volume data from 21 hydrological stations. Consistent with the IPCC's risk assessment formula—Risk = Hazard × Exposure × Vulnerability—the framework incorporates both social and ecological indicators. Human exposure and vulnerability indices are constructed using gridded data on population density, GDP, human development index (HDI), built-up land area, and water usage across multiple sectors. Ecosystem exposure is quantified through the Normalized Difference Vegetation Index (NDVI), while ecosystem vulnerability is represented by spatially distributed soil erosion rates, derived using the Revised Universal Soil Loss Equation (RUSLE). The spatial analysis reveals that the Fenhe, Jinghe, Weihe, Qinhe, and Yiluo River basins are flood-prone hotspots, particularly under scenarios where peak flows and volumes exceed design thresholds simultaneously. These areas are characterized by high population density, rapid urban expansion, and pronounced soil degradation, especially in the Loess Plateau. Conversely, upstream and central regions exhibit lower flood risk due to less intense rainfall, reduced anthropogenic pressure, and greater hydrological buffering. Importantly, the study finds that while human exposure is the dominant driver in most areas, ecological vulnerability—particularly soil erosion—plays a critical role in shaping flood response patterns through its influence on runoff generation and sediment dynamics. This integrated approach enriches the theoretical and methodological foundation of flood risk science by addressing the coupled dynamics of human and ecological systems. The framework not only enhances the predictive capacity of risk assessment but also provides actionable insights for policymakers and practitioners involved in flood mitigation, land-use planning, and ecosystem restoration. Ultimately, this study offers a replicable and scalable methodology that can support sustainable water-related disaster governance in complex socio—ecological environments.