The study analysed the effect of firecracker setting off on the fine particle pollution in city during the Spring Festival, based on the data of the mass concentration and the component of PM2.5 on Caochangmen(CCM) monitoring station in urban Nanjing and Guchenghu(GCH) monitoring station in suburb Nanjing. The results indicated that, during the firecracker setting off on the New Year's Eve and the 5th of Jan. In the lunar calendar period, the mass concentration of PM2.5 rose abnormally on CCM station, and its actually hourly maximum concentration were 2.79 and 6.02 times higher than the concentration on GCH station. The concentration of water soluble ions(K+,Cl-,SO2+4) and the elements(K,Al,Mg,Fe,Ba) of PM2.5on CCM station were higher than the concentration on GCH station. As a result, the firecracker setting off can dramatically affect the air quality in urban Nanjing during the Spring Festival.