In recent years, rainstorm chain disasters occurred frequently in megacities in China, seriously threatening people's life and property safety and social stability. Therefore, it is essential to take effective measures to timely break the chain and mitigate the disasters. This study thoroughly analyzes the disaster chain system of rainstorms and studies the trend deduction model of waterlogging disasters and the important role of various deductive simulation results in intercepting the disaster chain. It also proposes a chain breaking idea of combining simulation deduction with comprehensive response and clarifies the response strategies of various emergency bodies in the disaster response in megacities. Moreover, an overall response idea based on the policy of preparation, supervision, simulation, connection, and rescue is proposed. In view of the key problems including multi-department plan coordination, multi-dimensional information aggregation, multi-level accurate warning, and multi-team linked dispatching, we propose the following countermeasures: completing the comprehensive plan system, constructing a monitoring and early warning network, improving simulation and deduction application, strengthening joint response ability, and boosting the accurate rescue ability. Furthermore, development suggestions are proposed from the following aspects: formulation of policies and regulations, compilation of standards, application of intelligent technology, promotion of intelligent early warning and directional release technology, and formation of a new pattern of "national emergency."