Abstract: To investigate the microphysical structure characteristics of fog on Lushan Mountain, observational data of advection radiation fog occurring from 12–13 April 2023, were selected to analyze the near-surface meteorological elements, boundary layer structure, fog microphysical structure characteristics, and the temporal evolution of the spectral scale distribution of fog droplets on Lushan Mountain. The characteristics of the spectral distribution of fog droplets were then analyzed and compared with those from other typical regions. The results showed that the fog process was influenced by radiative cooling and warm moist advection, and was therefore classified as an advection-radiation fog. Near-surface cold advection, surface long-wave radiative cooling, and warm and wet advection transport in the middle and low layers (100–800 m) were all involved in the fogging process. The fog dissipated mainly in relation to the destruction of the lower temperature inversion caused by the enhancement of shortwave radiation and near-surface warming. The number and concentration of droplets were the highest during the formation stage and mainly comprised small droplets with a particle size ＜10 μm, and the amount then continued to decrease with fog development. The liquid water content continued to increase during the formation, development, and mature fog stages, and the highest content was reached in the mature stage. The droplet size increased gradually during the fog development process, reaching a maximum prior to fog dissipation. The concentration spectrum of droplets showed a bimodal distribution, with the main and secondary peaks at 6.5 and 15 μm, respectively. The liquid water content of droplets showed a trimodal distribution, with peak values at 6.5, 10.5, and 19 μm. Compared with 2016–2017, the droplet spectrum broadens, with enhanced contributions of both droplet number concentration and liquid water content in larger size ranges. and the proportion of large droplets increased. The droplet number and concentration were lower than that of Nanjing city fog and land fog in Donghai County, Jiangsu Province; the liquid water content was higher; the droplet particle size was larger; and the area was less affected by human activities and relatively clean. These results are useful for improving our understanding of mountain clouds, and they provide a scientific basis for conducting physical examinations of cloud seeding and fog dissipation.