A continuous heavy fog event along with a thunderstorm process in Guangzhou Baiyun Airport on 12 March 2014 is investigated by using the conventional observation data and WRF model simulation. The results show that the lowlevel southerly warm and wet flow provided sufficient moisture and wind conditions for the formation of this fog process; the sufficient moisture and the longtime inversion on the near surface layer were the main causes for the durative heavy fog. The inversion and the atmospheric saturation state were destroyed by the north wind moving down along with the cold front, which was the dynamic factor of the heavy fog disperses. The spatial distribution and hourly heighttime sequence diagram of water vapor content simulated by WRF can be used as references for forecasting the formation, maintenance, and dissipation of heavy fogs. The thunderstorm occurred under the background of high trough, shear line, and surface front, which was triggered by the combined action of 850 hPa shear line and the surface front.