A comprehensive system was developed to meet the demand of the security guarding during the 2008 Beijing Olympic Games. In the system, meteorological models, namely, MM5 and RAMS6.0, and a poisonous Clouds Diffusion Model over complex terrain (CDM) were configured in a one-way off-line nested way. In the system, MM5 runs were performed in a real-time operational way with a horizontal resolution of 3 km, which took the output from a global scale model，that is T213 from the Chinese Meteorological Administration（CMA), as the initial and boundary conditions, and the output from MM5 was used to drive the RAMS6.0 runs to provide a 36-hour prediction with a horizontal resolution of 500〖CD*2〗1000 m. The wind and turbulent field outputs from RAMS6.0 were sequentially used to drive CDM runs, which can provide the prediction of the concentration field and the dose field of the chemical clouds. During the 2008 Beijing Olympic Games, the system was used to provide the scenario prediction results and the security target was set as the National Stadium (known as the Bird’s Nest), and the quantitative analysis of the hazard risk was performed based on the scenario prediction results.