The performance assessment of a sustainable urban drainage system (SUDS) involves multiple criteria and is important for the decision-making of urban sustainable development. In this study, we intend to balance the comprehensiveness and objectivity in the performance assessment of SUDS development through a combination of multi-criteria decision-making (MCDM) analysis and mathematical quantification. We proposed an MCDM framework with eight quantifiable indicators, including flood mitigation capacity, pollution control capacity from technical criteria, life-cycle cost, damage cost, recreational function from socioeconomic criteria, biotope area ratio from ecological criteria, and spatial consistency from political criteria. A city-scale model based on engineering datasets and satellite images was created to implement gray and green infrastructure strategies in the studied area. Results revealed that gray strategies performed better in hydraulic improvements, mitigating approximately 17% of flood magnitude and decreasing over 20% of flood-induced damage. Green strategies were more eco-friendly, removing approximately 60% of non-point pollution and improving at most 15% of the ecological level. Integrated assessment demonstrated that the combine-used strategy showed the overall best performance, with a sustainability index of 0.676. Therefore, the methods and results in this study could provide additional improvements in the decision-making process of SUDS development.