Abstract:Based on the visibility data of 99 weather stations in Hebei Province during l980 to 2010, the change characteristics of low visibility events were analyzed, providing references for the environmental protection and comprehensive management in Hebei Province. The results show that the low visibility days appear fewer in northern Hebei， but more in southern Hebei, especially in the eastern part of Taihang Mountains, where the top 6 cities with the most low visibility days are located. In 1980s, the low visibility events are relatively fewer, but have a rapid growth in 1990s, then along with the attention to environmental protection, the low visibility days have been dropping since 2000. Comparatively, the low visibility days in December and in January are more, occupying 37.9% of a whole year, but are fewer in May and June, accounting for about 5%. The weather stations that show an increasing trend of low visibility days are mainly located in the eastern part of Taihang Mountains and southeastern part of Zhangjiakou where the industry is developed and the transportation is convenient. The weather stations showing a decreasing trend of low visibility days are mainly located in the plateau of north of Hebei Province and Hengshui Region， as well as the coastal areas of Qinhuangdao and Cangzhou. The relative humidity and visibility have a remarkably negative correlation. The events of visibility under 2 km are seen mainly in the days with the relative humidity above 80% while the events of visibility above 5 km are mainly appear when the relative humidity is under 60%.