Aiming at the problem of insufficient research on the transmission mechanism and blocking measures of urban flood disaster chain, this paper systematically identifies the disaster causing factors, disaster pregnant environment, disaster bearing body, response measures and other elements of urban flood disaster, explores the key elements of the flood disaster chain and their interactions, analyzes the occurrence and development process of the disaster chain, constructs a Bayesian network model of the key elements of the disaster chain, and conducts a case study in combination with the inundation event of the Beijing Guangzhou Expressway North Tunnel in the “7·20” rainstorm in Zhengzhou. The marginal probability analysis results show that the probability of serious ponding in the north tunnel of Beijing Guangzhou Expressway under the “7·20” rainstorm in Zhengzhou is 0.482, and the probability of causing serious casualties and vehicle losses is 0.434 and 0.558 respectively. The joint probability analysis of response measures shows that if the emergency plan, traffic dispatch, and professional rescue are not implemented in a timely manner, the probability of serious losses is the highest, which is 0.494. Timely response measures can significantly reduce the probability of serious losses, among which the comprehensive disaster reduction capabilities of the implementation level of contingency plans, rescue efficiency, and traffic dispatch speed decrease in sequence. Timely implementation of three disaster relief measures reduces the probability of the most serious casualties and vehicle losses to 0.152.