Abstract: In order to study the characteristics of wind field and pollutant transportation in a block,the wind field and pollutant concentration were simulated based on the computational fluid dynamics (CFD) software FLUENT using the RNG κ-ε turbulence model.A non-isolated three-dimensional (3-D) parallel block with a linear pollution source in the center of the street was taken as the research object,which was close to the real.The numerical scheme was validated by a wind-tunnel experiment,and then the distribution characteristics of flow field and pollutant concentration in the inner and downstream areas of the 3-D block on a micro scale were analyzed and demonstrated.The results show that the blocking effect of building group results in vortex area with low wind speed in the downwind direction and leads to high loads of pollutants from the inner block.The area of maximum wind speed exists nearby the entrances of two main roads due to the narrow tunnel effect,corresponding to the lowest pollutant concentration.A clockwise-rotated vortex appears in the street canyon with a ratio of height to width of 1:1,and pollutants mostly accumulates in the bottom of leeward,which is consistent with previous studies.The diffusion of pollutants is closely related to turbulence intensity and wind speed.Low pollutant concentration usually appears at the windward with intense turbulence and strong wind speed,while high pollutant concentration exists at the leeward.This work can provide a scientific basis for the city planning and alleviate the air pollution in populated urban areas using natural wind.