With the increasing expansion of city size and land prices of the city center,tidal flow congestion gradually becomes populated.Tidal flow makes the pollutant concentration increase rapidly in the jam side,and the pollutant distribution in the street canyon also becomes different.In this work,the numerical simulation was performed to explore the pollutant distribution character when the pollutant sources are uneven distribution.A comprehensive mathematical model describing the fluid flow and mass transfer characteristics were presented,and the influences of pollutant emission ratio and ambient crosswind speed were considered.The results showed that pollutant emission ratio has great influences on the pollutant distribution in the street canyon.The pollutant concentration at the pedestrian level increases uniformly both in the leeward region and in the windward region when the emission ratio increases from 1/4 to 1 on the windward side.Conversely,the increasing emission ratio from 1 to 4 in the leeward region only affects the pollutant dispersion in the leeward region.Besides,the higher traffic volume on the windward side may delay the pollutant dilution on the leeward side though ambient wind speed is increased.