Using the observation data of PM10 from April 2001 to May 2006 in Xi’an, an analysis is made of the temporalspatial distribution and seasonal variation of PM10 by means of statistical methods. The results indicate that pollution mainly occurs in winter and spring, and pollution is more serious in urban areas than in rural areas, in industry areas than in resident areas. Over the past five years, the most serious pollution occurred in 2002, and the number of days with PM10 exceeding the standard value was up to 190. A persistent heavy pollution event from 9 to 21 December 2002 in Xi’an is studied in detail, which was resulted from the stable PBL stratification and the local smallscale system in the near surface under the condition that the wind speed was low and the air relative humidity was large in the surface; Xi’an was controlled by the zonal westerlies at 500 hPa; and the surface homogeneous pressure system moved eastward slowly.