Abstract: Refined assessment of urban flood resilience is of great significance for guiding the construction of resilient cities. Based on the “4R” resilience theory (robustness, redundancy, resourcefulness, and rapidity), this study establishes an evaluation index system of urban flood resilience that integrates both natural and social dimensions. By coupling hydrological–hydrodynamic simulation, flood risk assessment, flood loss estimation, and spatial accessibility analysis, an empirical study was conducted in the Yunxi Plain of Hangzhou. The impact of the South Drainage Deep Tunnel project on resilience enhancement was also examined, and the relative contributions of various influencing factors to urban flood resilience scores were revealed using the XGBoost algorithm. The results show that urban flood resilience exhibits significant spatiotemporal variability: resilience declines rapidly during the flood peak, followed by a fluctuating low stage and gradual recovery, presenting a typical “decline–recovery” dynamic response process. The deep tunnel project substantially improves regional resilience, increasing the proportion of high-resilience areas (Grades IV and V) from 33.5% to 49.7%, and enhancing both disaster-bearing capacity and recovery efficiency. Attribution analysis shows that natural factors contribute 75.44% to overall flood risk, while social factors account for 24.56%, with inundation depth, inundation duration, drainage pipe density, and rainfall intensity identified as dominant drivers. This study provides a refined methodological framework for characterizing urban flood resilience, improves the spatial resolution of resilience assessment, and offers technical support for enhancing integrated urban flood disaster response capability.