According to the daily data of conventional surface observation from 1981 to 2010, the API and meteorological observation data of the same period in 2014 in Xingtai, using the method of the corrected Pasquill and the national standards, the atmospheric stability and the mixed layer thickness are calculated. The results show that in recent 30 years, atmospheric instable type shows growth trend and neutral type assumes drop tendency in Xingtai, with the change rates of 116% and -140% per 10 years, respectively. The diurnal variation of atmospheric stability under the influence of solar radiation is obvious, and the monthly change for neutral and stability types had the highest frequency. The wind is the important factor to determine the atmospheric thickness. The average thickness is 46009 m, and the monthly change shows a unimodal distribution. The daily variation of thickness has the characteristics: spring > winter > autumn > summer. The verification indicates that the mixed layer thickness and the occurrence frequency of various stability grades are the important factors affecting the air quality.