Urban air environment is a complex system with multiple objectives, multi levels and multiple factors. In this paper, the grey analysis of atmospheric environmental system is carried out, and the grey differential equation of air pollution is established, and the calculation method analysis and model verification of the grey numerical model are carried out. The relationship between the model parameters and the numerical solution is mainly analyzed, and the concentration field of the pollutant diffusion in the unsteady state is plotted. In this paper, the atmospheric environment system is analyzed from the grey system theory, and a more objective grey mathematical model is set up to carry out the Grey Numerical Simulation of the air pollution diffusion in urban area. It is of great practical significance to the flexible management and decision of air pollution control.