Hydrodynamics based numerical model is an effective way to simulate the movement of flood and its result can be visualized by many post-processing softwares. However, most of these tools are available only as local applications. This both limits the accessibility of the software to a specific machine and collaborative research. In this paper, we introduce a four-layer architecture for web-based visualization of numerical model. The application uses VTK(Visualization Toolkit) to render the numerical result and then the VRML standard is used to provide dynamic features over the web. By developing web-based visualization tools, it is possible for users to access the situation of flood wherever the internet is available, and can largely promotes the public services such as flood risk management.