Based on regular meteorological data from ground observations, regular sounding data in Sheyang, and the vertical data observed by rotorcraft Unmanned Aerial Vehicle (UAV), the boundary layer characteristics of a heavy fog occurred in Eastern Jiangsu from October 19 to 20 in 2019 was systematically analyzed. According to the vertical data from the rotorcraft UAV and the turbulence parameter Ri, it is found that a strong temperature inversion occurred near the ground during the periods of formation stage and maturity stage of the fog, moreover, the maximum inversion intensity reached 4.6℃/(100 m). From the formation to the development stage of the fog, the inversion gradually strengthened and the height of weak turbulence region also gradually increased. To be specific, the maximum height reached 280 m and thickness of the fog layer gradually increased with time. In the mature stage of the fog, the height of inversion layer reached the maximum of 250 m, meanwhile due to the influence of solar radiation, the intensity of inversion began to weaken, the upper turbulence of inversion layer began to increase and the height of the weak turbulence area decreased to 150 m. During the dissipating stage, the temperature inversion weakened and the thickness of the fog layer decreased rapidly. Meanwhile the turbulence increased and the inversion layer tended to dissipate gradually. During the period of fog formation, strong southeast wind occurred above the temperature inversion layer. In this case, the transportation of warm and humid air over the sea not only strengthened and maintained the temperature inversion, but also promoted the condensation of water vapor on the cold underlying surface, thus the heavy fog formed in the eastern coastal area. The vertical observation of UAV completely obtained the change characteristics of the boundary layer structure during the fog process, and the calculation of Ri well reflected the change of the height of the stable layer during the fog.