Abstract: Based on the observational data of thick fog from 679 base stations of China in 50 years, the basic climatic characteristics of fog in our country in temporal and spatial distribution are analyzed. In general, the distribution of fog in our country presents the characteristics of more fog in the southeast part while less in the northwest part. The spatial difference between south and north, west and east as well as the obvious regional characteristics can be shown in the distribution of monthly day numbers with fog, monthly maximum day numbers with fog and the seasonal distribution of fog. The analysis indicates that in most areas of our country, the day numbers with fog have a decreasing trend, but the annual change of days with fogs is not obvious. The initial study on the change of days with fog has also been made in this paper.