Based on the meteorological data from conventional observation stations, a typical large-scale regional heavy fog process in Henan Province from the night of 11 to the day of 12 March 2021 is analyzed. The study focus is on the analysis of the time characteristics and explosive enhancement characteristics of the heavy fog process. The results show that this heavy fog process had the characteristics of explosive enhancement. The explosive enhancement time at 40 typical heavy fog stations was less than 30 min, with an average of only 9.5 min. The high humidity environment caused by the precipitation ahead of the fog and the clear-sky radiation cooling over night provided important conditions for triggering and strengthening the heavy fog process. Large-scale breeze or even calm wind near the surface was another favorable condition for explosive development of this fog process. In addition, the transport of warm advection near the surface was also an important cause for the explosive development and maintenance of the heavy fog process. According to the variation of visibility, two types of heavy fog explosive enhancement are divided, i.e., jump-burst type and direct burst type, in which wind played different roles. In the former, the effect of wind caused turbulence diffusion and affected the dramatic fluctuation of visibility, while the latter had warm advection transport under the action of wind, which was conducive to the development and persistence of the fog.