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In this paper, the spatial, temporal distribution, transformation and source simulation of NO3- were analyzed systematically based on the monitoring data, literature review and numerical simulation (CMAQ4.7.1). Analysis results showed that annual average concentration of NO3- in Beijing was between 6.69 and 12.48 Mg/m3 with an increasing trend in recent years; concentration of NO3- in Beijing in 2013 was higher in winter and autumn than that in spring and summer and diurnal variation of NO3- showed bimodal distribution and spatial distribution of NO3- showed significant north-south gradient distribution; annual average N0R in Beijing was between 0.12 and 0.17 while it was between 0.17 and 0.20 during heavy air pollution days in 2013; the average ratio of NO3-/S02- was between 0.97 and 1. 06 while it was between 1. 00 and 1. 07 during heavy air pollution days in 2013; the emission sources of Beijing was being changed from fixed source to both fixed and moving sources in feature development; simulated local, external transportation, background and boundary condition were 40%, 44% and 16% respectively to the annual average concentration of NO3- in Beijing in 2013 while they were 31%, 57% and 12% respectively in heavy air pollution days, which indicated that external source played an important role to the concentration of NO3- in Beijing. [ABSTRACT FROM AUTHOR]