A meteorological numerical simulation system for urban emergency service is established， according to the needs of urban emergency responses. There are two main models included in the system： Pollution Diffusion Rapid Numerical Prediction Model （PDRNPM）， which is mainly based on MM5 and RAMS 6.0， and Rapid Emergency Meteorological Service Software （REMSS）， which is based on the urban subdomain model and the Gauss model. PDRNPM is better for its precision and predictability， allowing the emergency staff to predict the gas diffusion situation of one hour later within 15 minutes. REMSS is easy to install， operate and give responses quickly， and can simulate gas diffusion within 2 to 3 minutes once emergency situation is triggered. Applied in the Beijing Olympics Games 2008 and Paralympics Games 2008 and routine emergency exercise of Beijing， it is proved that the system can well meet the demands of emergency command due to its time effectiveness and applicalibility and can provide reliable realtime references for the Beijing Emergency Commode Center.