There were some fog hazy days accompanied by serious long-term air pollution in the southern Hebei Province during January, 2013. The weather conditions, atmospheric environmental background and mechanism of formation for heavy air pollution were analyzed based on daily data, including air quality index (AQI), routine weather observation and spatial grid 1°×1° reanalysis of NCEP. The results showed that the weather factors were abnormal in January, 2013, by showing low air temperature at 1-2℃, relative humidity higher 15%, short sunshine hours less 40% than under normal condition, and more rainy days with little amount. The hazy days often occurs in the middle and south part of Hebei Province, since the water and air pollutants easily meet when surface wind speed was weak and both wind speed and direction focused on the ground. Abundant moisture and pollutants with high humidity of boundary layer could carry each other. In addition, strong temperature inversion layer, dry warm cover in the lower atmosphere, and sinking motion in the boundary layer prevent water and pollutants diffuse to the upper air. The stable atmospheric circulation feature provided favorable environmental field for hazy weather and heavy air pollution. The special geographical condition in the south Hebei Province was an important factor for the fog haze and pollution lasting. Stable west wind in low level sunk to the east of foothills of the Mountain Taihang after across the mountain, and easily formed convergence lines in the plain areas, and further aggravated the gathering of water and pollutants in the ground layer.