Based on the conventional observation data, NCEP geopotential height and wind reanalysis data from National Centers for Environmental Prediction, the process of fog is analyzed by taking use of the method of synoptic meteorology. It turns out that there are three types of synoptic situation at 500 hPa when the regional fog around the Bohai Sea coastal areas occurs, which are zonal flow, low trough, high pressure ridge, and four types of surface synoptic situation, which are frontal cyclone, high pressure forepart, uniform pressure field and weak high pressure. According to the characteristics of the ridges and troughs, high and low pressure centers, an objective and automatic identification system is designed. Furthermore, multiple moisture condition, stratification stability condition and wind speed condition are calculated on the basis of T639 model output. The 1000 hPa depression of dew point, 1000 hPa wind speed, temperature difference between 925 hPa and 850 hPa, and M index are selected as physical diagnosis factors after diagnostic and correlation analyses. Thus, a forecasting system combining automatic identification of synoptic situation and T639 is established, which can forecast the space and time of the fog around the Bohai Sea coastal areas within the next 1-3 days. Experimental results show that good results have been achieved.