Air flow and pollutant dispersion characteristics in a real valley city are studied under the real boundary condition.The 3D computational fluid dynamics using Reynolds-averaged Navier-Stokes modeling was carried out in Lanzhou which is a typical valley city in Northwest,China.The standard κ-ε turbulence model as a simplified computational fluid dynamics model is used to provide moderately fast simulations of turbulent airflow in an urban environment.The modeled flow field indicated that the geometry,wind direction and source location had a significant effects on the flow field.The flow shows the funnelling is rather obvious when the wind flow through the narrow area in the middle of the city.It is obvious that in the high-altitude region,due to the impact of high and low differential pressure and terrain,SO2 and NO2 formed two cyclic concentration field in the dispersion process.