A comprehensive field observation of fog in both the center and suburb of Chongqing is carried on in December 2001,there were two processes of fog in 4th and 29th during that period.By analyzing the two processes of fog,the macro- and micro-physical characters of Chongqing fog in winter are revealed,and the new characters of Chongqing fog after the development of the city are obtained by comparing with the Chongqing fog ten years ago.At last the reason for such change of Chongqing fog is also analyzed.In comparison with the Chongqing fog ten years ago,the duration of fog is shortened,the intensity weakened,and the erupting development postponed;the density of fogdrops is about ten times and the size of fogdrops is one half.The expansion of the city,the reduction of humidity,and the increase of aerosal particle concentration are responsible for such changes of Chongqing fog.