Based on meteorological data from 70 automatic weather stations and 365 traffic meteorological observation stations of Jiangsu Province, a heavy fog process that occurred in Jiangsu in 11-12 February 2016 is investigated. The results show this fog process features that the fog formed and intensified explosively. At most stations, the dense fog formed rapidly with the visibility dropping directly from 1000 m above, and there was multiple burst enhancement phenomena in some areas. Along with the opened sky at night, the longwave radiation cooling also strengthened, which was an important cause for the formation and explosive development of the wide range of heavy fog. Meanwhile, the prophase rainfall provided basic conditions for the formation of the heavy fog, and also was the direct cause of the enhanced evaporation and explosive increase of heavy fog at some sites after sunrise. In addition, strong inversion temperature provided stable atmospheric conditions for the explosive development of fog. The lowlevel jet near the top of inversion temperature promoted the maintenance and enhancing of the strong inversion, which played an important role in the explosive development of heavy fog.