The temporal and spatial distribution characteristics of the low horizontal visibility (lower than 1000 m) in Beijing are studied, which is chosen as an index that would affect urban traffic and transportation. According to both mean daily variation over many years and mean daily, monthly and seasonal variation in a year of low visibility frequency, Beijing is divided into three different parts, the southeastern plain area, the northwestern mountainous area, and northeastern to southwestern transitional area. The effect of some synoptic phenomena, such as fog, fly ash, and so on, upon the low visibility in Beijing is also discussed. It is shown that fog is the main factor affecting visibility.