The spatio-temporal characteristics and pollution sources of NO2 in Nanjing metropolitan area are analyzed by using cosine curve function and HYSPLIT model of back trajectory analysis, on the basis of NO2 column densities data of the Ozone Monitoring Instrument (OMI) from January 2006 to December 2014 and land use type data. The results indicate that tropospheric NO2 column densities in study area increased distinctly year by year from 2006 to 2014 and showed obvious seasonal variation, i.e. highest in winter while lowest in summer. There are mainly two aspects of tropospheric NO2 contaminant sources in study area. The one is the effect of atmospheric transport affecting the seasonal variation of NO2, and the other is that different land use types have great impact on column density of NO2.