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Based on the conventional observational data，the observational PM2.5 concentration and NCEP reanalysis data, a comparative analysis is conducted on the atmospheric conditions, boundary layer characteristics of two serious air pollution events which took place in 2013 and 2016,respectively. The results are: (1) At 500 hPa, the processes of 2013 and 2016 were controlled by the blocking circulation and zonal circulation, respectively. The Guanzhong area was affected by the westerly flow; the surface pressure field was weak, and the atmospheric stratification was relatively stable. (2) In the 2013 event, the inversion layer near the ground in Xi’an was low; the relative humidity was high; the temperature was low; which is not conducive to the vertical turbulence exchange and in which the pollutants were easy to accumulate. It is one of the reasons that the process of 2013 heavy pollution lasted longer and the concentration of pollutants was higher than that of 2016. (3) Both heavy pollution processes in Xi’an had the significant low wind speed characteristic, and the northeast wind was the dominant wind direction. The 2013 process is the result of the combination of local pollution accumulation and upstream pollution transmission. (4) The process of 2013 was affected by cold air, and the continuous dry and cold northeast wind made haze dissipate in the Guanzhong area; while the process of 2016 was affected by the plateau trough, and rain and snow weather made pollutants deposite and haze dissipate.