The WRF/Chem model coupled with anthropogenic atmospheric pollution emission data from NCAR is used to simulate characteristics of one pollution event in Beijing on 31 August 2012. The results show that ozone (O3) concentrations have obvious diurnal variation characteristics. The high and low peaks appear in the afternoon and night respectively. The spatial distribution and flow field are related. PM2.5 also has the diurnal variation, but the spatial distribution is relatively stable and mainly in urban areas. Local pollutants have horizontal transport characteristics but the total amount is about zero, and it has not increased the local accumulation of pollutants. Long distance transportation from southern Beijing is one of the main sources of the pollutant. Sensitivity test analysis shows that the O3 pollution of the process is mainly from Beijing, and the fine particles are mainly generated locally. The sensitivity of O3 pollution to the nitrogen oxide (NOx) is relatively stable, but varies greatly to volatile organic compounds, especially from wee hours to morning.