Comprehensive fog observation campaigns at Lushan Meteorological Bureau of Jiangxi Province were conducted with a fog drop spectrometer and an automatic weather station in January and December of 2016, respectively. This study investigated the physical characteristics (macro and micro) of supercooled fog and elucidated its evolution mechanism. Combining observational data with NCEP 1°×1° reanalysis data, the macro and micro physical characteristics of two supercooled fogs cases (case 1 on January 16-17, 2016, while case 2 on December 25-27, 2016) were analyzed. Our results revealed that the evolutions of the two supercooled fogs were strongly correlated with the movement of cold front. From the formation stages to the development stages, the dominated wind direction below 800 hPa changed from southwest to northerly, the front edge of the cold front arrived at the study area, and the temperature near the surface decreased sharply in both cases. At the mature stages of the two supercooled fogs, the rain stopped at the near-surface and the wind force weakened, meanwhile, the front inversion layer appeared in case 2. During the dissipation stages, the wind direction in 900-500 hPa changed into north in both cases and the wind speed below 800 hPa increased obviously. For micro characteristics, the average droplet spectra exhibited bimodal distributions in both cases, with the main peaks at 4.9 μm. However, the secondary peaks were at 8.9 and 11.0 μm in case 1 and case 2, respectively. Both cases presented instantaneous droplet spectra with the main peaks between 10 to14 μm, and the frequency were 12.4% and 46.3% in case 1 and case 2, respectively. Both cases had a transition from warm fog to supercooled fog. Compared with the warm fog, the number density of supercooled fog droplets in each size increased, especially for droplets with particle size below 14 μm. The correlation between fog droplet number concentration and average diameter in the whole process of case 1 was weak, which may be affected by factors such as fog droplet collision-coalescence and droplet competition for water vapor. Case 2 showed positively correlation among the fog droplet number concentration, average diameter and water content in the whole process, which indicated that the fog process was dominated by condensation nuclei activation and condensation growth. The strong low-level jet in southwest, the obviously decreased temperature in near-surface, and the inversion layer were all found in case 2, resulting in the wider droplet spectrum, the more prominent peak between 10 and 14 μm particle sizes in droplet spectrum, moreover, higher values of number concentration, average diameter, and water content comparing with case 1.