Abstract:We analyzed space and time distributed characteristics of poor visibility frequency and the changing situation of its interrelated meteorological factors by using the ground station data as well as the upper air and the earth’s surface data in the region of Bohai Rim. The results have shown that the characteristics in the interannual change of poor visibility present a weak upward trend and periodic oscillations, with main periods of 2 a， 4 a and 6-8 a.The frequency of poor visibility has two peaks in a year and one peak in a day at local time 08 h. The spatial distribution of low visibility’s frequency exists a great inconformity. According to the different spatial distribution in the seasonal frequency of poor visibility, the whole region can be divided into three areas. It seemed that high humidity and light wind are the main meteorological conditions prone to produce low visibility. While the early or the same time as the appearance of poor visibility, these conditions maintain an inversion or isothermal layer and wet layer in the lower atmosphere.