Abstract: Based on the meteorological observations and air quality data obtained from environmental monitoring center in Changzhou from 2001 to 2011,the characteristics of haze and its impact factors were analyzed in this study.The results indicate that annual cumulative haze days fluctuate largely.The occurrence frequency of haze is larger from November to January,and smallest in summer.Haze occurs most frequently at 11:00,followed by 14:00,and least at 05:00 in order.The haze formation is usually accompanied with two weather types at upper atmosphere,and three weather types near the surface.Haze dose not occur under strong rainfall conditions,but sometimes occur under weak precipitation conditions.The inversion layer favors greatly the haze formation.Haze in Changzhou usually occurs under conditions with weak easterly winds under 2 grades and with relative humidity between 41.0% and 70.0%.The fog-haze transmission always exists in most of fog events (except rain-fog).There is very close relationship between haze,CO,and PM₁₀ from 2001 to 2011 at Changzhou.According to a haze case,it shows that the straw burnings,pollutants transported by winds,and air descending motions are major reasons for this haze process.