<p>Climate change and urbanization exacerbate flooding and pose challenges to environmental management. Green infrastructure (GI) has attracted the attention of policymakers and planners due to its effectiveness in mitigating flooding, minimizing social disruption, and improving urban flood resilience. Flood resilience can refer to an urban system’s capacity to withstand, adapt to, and recover from flooding disturbance. Assessing the effects of these mitigation measures on flood resilience is essential to address flooding. However, existing performance-based flood resilience metrics neglect the enhanced ability of the physical environment to manage flooding with GI implementation. A system should perform better after implementing GI for the same surface inundation level, but current quantitative metrics do not capture this. These hinder the accurate revelation of resilience-enhancing effects of GI. Furthermore, few studies have sufficiently evaluated the effects of GI on improving flood resilience in different deployment areas from the perspective of system functionality dynamics during flooding. This study proposed a novel performance-based metric that accounts for the resilience-enhancing effects of GI and conducted comparative analyses across different scenarios. The results indicate that GI enhances system performance and reduces the duration of system performance being impacted in severely inundated areas. Implementing GI in the ex-situ scenario does not necessarily improve the adaptation and recovery rates. The in-situ impacts of GI are more pronounced in terms of the system’s functioning in the most unfavorable state, the recovery from the most unfavorable state to the equilibrium state, and the adaptation and recovery rates.</p>