Abstract: For slated roof shape in the street,the effects of different wind speed and different window opening percentage on the flow and diffusion of pollutants were studied by CFD numerical simulation. The results showed that the air vortices in the canyon were mainly concentrated on the top of the windward and leeward surfaces. The pollutant concentration index on the windward side was much less than that on the leeward side. Increasing the wind speed and the window opening percentage would reduce the pollutant concentration and the flow vortex in the whole valley tended to decrease and disappear.