Abstract: Affected by global warming and accelerated urbanization, extreme rainfall events in cities have occurred frequently in recent years, resulting in waterlogging. The numerical simulation results of urban stormwater based on hydrological and hydrodynamic models are difficult to show the problems of rainfall and waterlogging gradation. Firstly, the GAST hydrodynamic model is used to simulate the stormwater waterlogging process, the numerical discretization method is carried out by Godunov type finite volume method, the GPU parallel technology is used to accelerate the calculation to obtain the numerical simulation results under different output times, the numerical simulation method of the GAST model and the digital elevation model data coupling method is innovatively designed, and the digital inundation grid model is constructed Model), based on WebGL and 3DGIS technology, develop a 3D reality dynamic visualization engine, build a 3D reality dynamic rendering mechanism for the rainwater waterlogging process, and simulate the dynamic 3D reality scene of the stormwater waterlogging process. Finally, the three-dimensional dynamic simulation expression of the second heavy rainfall waterlogging process in Xi'an on July 10, 2020 is realized by this method, and the results are vivid, intuitive and accurate, and the degree of agreement with the measured results is high, indicating that this method can effectively make up for the shortcomings of the existing numerical simulation expression methods of urban stormwater waterlogging, and has good application value.