A continuous heavy fog process and air pollution occurred in East China during 7〖CD*2〗11 January 2008. Based on the synoptic data, NCEP/NCAR reanalysis data set and MM5 model outputs, the surface circulation, water vapor condition, dynamic factor, temperature stratification, and air quality are analyzed in detail. It is concluded that the surface moisture flux divergence, vertical velocity, and the divergence difference between 1000 hPa and 500 hPa are not significantly correlative with the visibility, while the relative humidity near the surface is significantly negatively correlative, the temperature lapse rate（γ）near the surface is significantly positively correlative with the visibility, therefore, RH≥85%、γ＜0.2 ℃·（100 m）-1 could be regarded as the necessary conditions of fog formation. In addition, the lowest visibility in Shanghai Hongqiao International Airport during the period of 0400 UTC on the previous day to intraday 0300 UTC is intensely negatively correlative with the Air Pollution Index （API） in the meantime. The API rising up to 150 could be an important criterion of fog formation in Shanghai Hongqiao International Airport.