Abstract: Urban flood disasters exhibit chain-like propagation characteristics, and analyzing the transmission laws and spatiotemporal evolution features of urban flood disaster chains is of significant importance for disrupting the disaster chain. This study aims to use two events from the "7·20" unprecedented heavy rain and flood disaster in Zhengzhou—the flooding of metro line 5 and the flooding of the Beijing-Guangzhou expressway tunnel—as case studies. A knowledge graph was constructed to reveal the transmission laws of the disaster chain. By reviewing the evolution process of the disaster chain, triggering points, detonation points, diffusion points, and amplification points within the disaster chain were identified. The study focused on analyzing the disaster-causing mechanisms and spatiotemporal characteristics of the disaster chain, presenting the impact levels of different disaster chains in the form of disaster curves. Analysis of typical cases of the "7·20" flood disaster in Zhengzhou indicates that there were several chances to break the disaster chains in both events. In the disaster relief process, the influence of pre-disaster and in-disaster factors should be comprehensively considered, and decisive measures should be taken to break the chain. It is crucial to fully leverage the timeliness of emergency measures, promptly block detonation and diffusion points, and reduce losses from flood disasters. This method can be applied to the retrospective analysis of chain-like disasters, guiding the analysis of the disaster-causing mechanisms and entry points for disaster relief in specific events.