The structure of commercial district buildings becomes more and more complicated and seriously affects the ventilation and the pollutant diffusion of surrounding buildings. By taking a building group of a commercial district of Chongqing as research object, based on threedimensional turbulence model, this article uses CFD software to conduct numerical simulation on the ventilation capacity and the diffusion of continuous emissionair pollutants of the building group, comparatively analyzes the impact of meteorological condition change and seasonal change on the ventilation and the pollutant diffusion of the building group on horizontal and vertical direction, and obtains that there is positive relation between the atmospheric mixing layer height and the ventilation capacity and pollutant diffusion rate of the building group. The research results can provide the reference for improving building ventilation effect and reducing pollutant concentration of the surrounding buildings.