The fog comprehensive observation data collected in the surface layer in northern suburb of Nanjing (32°12'N,118°42'E,25 m a.s.l.) in winter from 2006 to 2009 are used to investigate the interaction between radiation characteristics and fog microphysical structure.Results show that,when the net radiant flux density lies between -50 and +25 W·m^-2,the fog droplet number concentration increases gradually and the fog droplet number density increases more significantly with the decrease of fog droplet size.It indicates that the surface radiation cooling or very weak heating can facilitate the activation and condensational growth of fog droplets.While the net radiant flux density is greater than +25 W·m^-2,the fog droplet number concentration declines significantly and the fog droplet number density reduces more rapidly with the decrease of droplet size.The solar shortwave reflectivity is strongly influenced by the fog droplet number concentration,mean radius,and liquid water content.During the fog events,while the fog droplet number concentration and liquid water content increased by 100 cm^-3 and 0.001 g·m^-3,the solar shortwave reflectivity would increase by 5.29×10^-3 and 1.18×10^-4,respectively.