Abstract: Based on the meteorological data from conventional observation stations, traffic weather stations and high-altitude ground data, a typical large-scale regional heavy fog weather process in Henan Province in spring from the night of March 11 to the day of March 12, 2021 was analyzed. A schematic diagram of the visibility change characteristic curve of this process was summarized and condensed. By analyzing the time characteristics and occurrence and development of the process of heavy fog, the results showed that there were mainly two types of visibility change curves in this heavy fog process. One was to first go through a period of violent fluctuations up and down and finally reached a strong dense fog and maintained it, and the other was to directly and rapidly exploded to form a heavy fog. At most stations,the heavy fog had the characteristics of explosive enhancement. The average action time for visibility to drop from above 1000 m to below 200 m was only 9.5 minutes. The average longest duration of the heavy fog was 193.6 minutes, and the longest was 459 minutes. The average action time of fog elimination was 35 minutes, which was significantly longer than that of explosive enhancement. The high humidity environment formed by the precipitation before the fog provided a good background condition for this heavy fog process. The cooling of the near-surface layer produced by net surface radiation fluxes was the triggering and explosive development mechanism for the fog event. Large-scale breeze (wind speed <1m s-1) or even calm wind near the surface layer was another favorable condition for explosive development of this fog process. At the same time, the near-surface wet advection transport was also an important reason for the explosive development and maintenance of this heavy fog process.