The characteristics of largescale circulation background and meteorological elements in fog events are studied, based on the continuous observations (wind, temperature, relative humidity and visibility) at automatic weather stations along the BeijingTianjinTanggu expressway from October to December in 2007 and the NCEP reanalysis data. It is found that the typical situation of local fog exists in the circulation of downdrafts in upper air and the weak pressure field on the ground; while the systematic fog exists in the region of thermal advection in the lower troposphere and weak pressure field in front of the cold front on the ground. The air temperatures are 9-13 ℃，4-7 ℃ and -6-1 ℃ in October, November and December respectively, during fog events. And humidity is mainly over 90% but partly between 85% and 90% for the visibility of 500-1000 m, with wind direction changefully and wind speed mainly less than 2 m?s-1. The huge differences of the formation and dissipation, duration and the sequence, occurring frequence for fogs at each section of the BeijingTianjinTanggu expressway are also obtained.