Abstract: With the increasing of vehicles in China, photochemical smog pollution accidents may be greatly possible in some Chinese cities. However, the predicting and alarming of photochemical smog is only in the preliminary stage. MODIS Information Service Processing System established by NASA provides 10km?10km resolution aerosol optical depth (AOD) Level 2 products. This paper establishes the framework of advanced warning mechanism system for the urban photochemical smog pollution based on MODIS data. The framework includes MODIS data reception and processing, analysis of variation of meteorology, analysis of ground surface detection data, atmospheric pollution index, and determination of advanced warning scale, etc. We can further develop advanced warning system on the existing framework process basis which is designed for urban atmospheric pollution aided monitoring and prediction and advanced warning of atmospheric pollution. There exists photochemical smog episode in some cities because of the increasing motor vehicles in China, which are more and more serious and dangerous. But the prediction and the early warning system do not start to work. So we had better monitored the photochemical smog using remote sensing data and built the early warning system at the same time. Some studies indicate that there is distinct positive correlation between aerosol optical depth (AOD) and air pollution monitoring by MODIS data. When AOD<0.3, air is clear, when 0.31.0 air pollution is serious. Based on correlation analysis between AOD and air pollution, using data of air pollution monitors and Air Pollution Index(API), this article divided early warning system of urban photochemical smog pollution into five grades: none, weaker, weak, strong, stronger, which can lay a base for the advanced warning system to the urban photochemical smog pollution. Advanced warning system of the urban photochemical pollution may be a part of the urban disaster prevention and reduction system to publicize atmospheric photochemical pollution in time, and provide grounds for controlling environmental pollution and reference information for our daily lives and outgoing.