Abstract: Flooding is a natural disaster that seriously endangers the safety of people’s life and property. Given the insufficient systemization of the existing flood disaster simulation technology in our country, it is difficult to visualize the situation, trend, and damage assessment of the flooding to the decision-maker instantly and intuitively. An interactive large-scale flood disaster dynamic scene early warning simulation system is implemented. Firstly, the semi-Lagrangian implicit integration method is used to quickly solve the shallow water equation under the premise of conservation of momentum and volume, which achieves real-time and stable simulation calculation of flood evolution. Secondly, a warning rule for building flood disaster crisis is proposed by changing the color of building to show the crisis level when flood is developing. Finally, an interactive large-scale flood simulation system is established, which contains functions such as adding baffle to show the area’s flood control and the effect of flood discharge caused by adding inlet and outlet, time-varying water level display of buildings and so on. The results of simulation experiment on the urban elevation data collected by us show that the system will provide an intuitive and reliable basis for the decision-making design of flood control and disaster reduction in the construction of a modern sponge city.