Abstract: In this study，PM2.1 were sampled at environmental monitor stations(Chongning and Wangzhuang stations)at all seasons(April，July，October，December in 2014)and during heavy haze days(January in 2015)in Wuxi.Characteristics of concentrations and chemical compositions were analyzed.A chemical mass balance(CMB)model was applied to apportion the contribution rate of different sources.The final results of source apportionment for secondary aerosols were obtained combined with the local emission inventory.Investigations show that the annual average concentrations of PM2.1 were 68.6 μg·m－3.The concentration at Chongning station was 71.9 μg·m－3 higher than Wangzhuang station(65.3 μg·m－3)．The concentration was 85.7 μg·m－3 in winter and lower at other seasons.During heavy haze days，the concentration was 122.8 μg·m－3，it was much higher than the annual average concentration.The dominant chemical constituents of PM2.1 were secondary inorganic aerosols(36.4%)and carbonaceous(29.1%)，during the heavy haze days secondary organic aerosols were much higher accounting for 38.4%.The generation，accumulation and aging of organic aerosols were very important to the higher concentration at heavy haze days.The results of source apportionment show that the contributions of emissions were secondary nitrate(26.4%)，secondary sulfate(22.6%)，secondary organic aerosols(7.8%)，coal(7.3%)，soil dust(6.5%)，diesel exhaust(6.4%)，gasoline vehicle exhaust(4.1%)，biomass burning(3.4%)，construction dust(3.3%)，the dust(2.5%)，sea salt aerosol(2.2%)，cooking(1.1%)，iron and steel smelting(1.0%)in turn.During heavy haze days，the contribution of secondary organic aerosols was higher than average，and was 12.3%.Combined with local emission inventory，the secondary aerosols were apportioned and the final contribution of emissions were coal-fired power plants(30.68%)，steel smelting(13.92%)，other industrial(10.48%)，biomass burning(3.49%)，gasoline vehicle exhaust(6.50%)，diesel vehicle exhaust(8.80%)，vessel(0.44%)，construction machinery(0.66%)，aircraft(0.03%)，construction dust(3.3%)and soil dust(6.5%)，the dust(2.5%)，cooking(1.1%)，seasalt(2.2%)，and other sources(9.40%)．With the secondary analytical calculation，we can see that the contribution of fine particles in Wuxi are mainly from coal-fired power plants，industrial smelting and automobile exhaust.As a result，we should develop clean energy vigorously and strengthen controls on coal-fired，industrial activities and automotive exhaust emission.