Abstract: Natural Disasters pose significant threats to urban sustainable development. Quantitative assessment of urban system resilience is essential for building disaster-resilient cities. This study, based on the“risk source-exposure-risk mitigation factor”theory of urban safety, conceptualizes urban systems as a three-layer coupled network comprising population, public service facilities and infrastructures, with disaster scenarios acting as external risk sources. A disaster mitigation model is established to simulate government emergency response and recovery capacity under disaster scenarios. From the perspective of urban system supply-demand imbalances within the urban system, a quantitative resilience indicator is developed, and a method for assessing urban system resilience is proposed. This study takes the medical system of Tangshan City as an example to evaluate the disaster resilience of the urban medical system under the impact of the Tangshan M_s7.8 earthquake, and compares the impact of disaster mitigation capabilities on system resilience. The results demonstrate that this method can effectively simulate the supply-demand interaction between disaster-bearing bodies, and quantitatively evaluate the disaster resilience of urban systems and the effectiveness of emergency recovery strategies. This study systematically integrates risk sources, the supply-demand of disaster-bearing bodies, and government disaster mitigation capabilities into the same evaluation framework, providing a new theoretical method for urban system resilience evaluation, which will effectively increase urban system resilience and grassroots emergency management capabilities.