The synoptic weather patterns and formation mechanisms of two large scale and severe haze episodes, which occured over Hebei province in early and middle October, was investigated by using pollutant concentration data from the Heibei environmental monitoring station, meteorological observations and NCEP reanalysis data, combining with the HYSPLIT4.9 backward trajectory model. The highest PM_2.5 concentration appeared in Xingtai, reached 507μg/m³. The visual range was less than 1km. The uniform pressure field and steady upper air circulation provided favorable meteorological conditions for two haze episodes. High relative humidity, small wind speed, and low mixing layer height result in an unfavorable meteorological condition for pollutant diffusion, which is the main cause of the two lasting haze episodes. Satellite fire map and air mass backward trajectory show that straw burning in southern Hebei and surrounding provinces exacerbated air pollution in two episodes. Transport of polluted air mass have significant impact on regional heavy haze weather.