To address the insufficient attention to cascading effects in current urban flood risk assessments, a risk assessment method for urban flood disaster chains with critical municipal infrastructure as the main disaster-bearing bodies is proposed. This method couples a flood simulation model with a system dynamics model, where the flood simulation model provides spatial and temporal inundation data to drive the system dynamics model for dynamic risk evaluation. A case study was conducted on the May 22 flood event in 2020 within the Nangang River Watershed of Guangzhou City. The results show that the exposure and hazard levels of different disaster-bearing bodies evolve differently. Water conservancy infrastructure, major chemical plants, hospitals and underground spaces showed high exposure, with peak values exceeding 0.65. Although bridges and tunnels showed lower exposure, the hazard level of their inundated parts can reach 5.63. A non-linear relationship was found between the comprehensive urban flood risk and precipitation. During the heavy rainfall on the early morning of May 22, the cumulative precipitation increased by 138%, while the comprehensive flood risk index increased by 816%, far exceeding the 215% increase in the exposure of disaster-bearing bodies. This method enhances the understanding of disaster chain risk and provides decision-making support for the formulation of flood alleviation strategies and emergency actions for critical urban infrastructure.