Abstract:ased on visibility, relative humidity, weather phenomenon and related other data in Nanjing during 1980—2008,by using percentile,grades and Ridit analysises, study is performed of the characteristics of visibility caused by only air pollution,excluding meteorological effects. Results show that both the yearly and seasonal visibilities have declined notably over the past 29 a. The trend of “bad” or “common” visibility goes up, “good” visibility trend declines, and the four seasonsvisibility and their distribution are characterized by that in spring(fall) visibilty change is remarkably different from that in summer(winter), in addition, the visibility is declining with decades and the visibility difference between seasons is also diminished. Furthermore, the visibility of winter becomes worse and worse since 1987, and in this century the visibilty in winter is mainly “bad” and “common”, and in the other seasons it is mainly “common”.