Abstract: Based on the ground observation data and ERA5 (0.25°×0.25°) hourly reanalysis data of Maotai Airport in Renhuai, Guizhou, the synoptic and diagnostic were used to comprehensively analyze the fog process at Maotai Airport from February 14 to 15, 2018. The results show that the fog was an typical advection fog. In the first half of the fog, the near-ground of the airport was mainly affected by warm advection, and in the second half, it was mainly affected by weak cold advection. The frontal transit had a temporary clearing effect on the fog. The whole process took place under the background of the pattern of higher in the west and lower in the east and the eastward movement of the southern branch trough. In the warm advection fog stage, the airport was influenced by the water vapor from the Bay of Bengal and the South China Sea, which created the water vapor conditions for the occurrence and maintenance of advection fog. In the weak cold advection fog stage, there was a convergence center near the ground, and the water vapor from the south converged with water vapor from Chishui River Valley to the northwest of the airport. The temperature inversion (or isothermal) layer over the airport in the fog process was the front area of the quasi-stationary front of Yunnan-Guizhou in winter. It stabilized the atmosphere, making it easier for fog to form and sustain. After the main body of cold air moved south to the northern part of Guizhou, the lower level subsidence movement caused by cold advection and the improvement of horizontal diffusion conditions were the reasons for the final dissipation of the fog.