Abstract: Using the hourly visibility and relative humidity data of 153 meteorological observation stations in Sichuan Province, the fog is divided into four levels according to the visibility: heavy fog, dense fog, strong dense fog and extra strong dense fog. The temporal and spatial distribution, duration time, generation and disappearance time of different levels of fog in Sichuan are analyzed. Studies have shown that the frequency of fog is most in winter and least in summer, and extra strong dense fog is rare from April to September. The most frequent time period for the four levels of fog is from 3: 00a.m. to 9: 00 a.m., and the least is from noon to night. Strong dense fog and extra strong dense fog rarely occur from1: 00 p.m. to 8:00 p.m. Sichuan Basin is a fog-prone area. There is less fog in the western Sichuan Plateau and Panxi area, and there is no strong dense fog and extremely strong dense fog in most areas of Sichuan. The heavy fog and dense fog in Sichuan lasts for a short time, generally 1~3 hours. Once strong dense fog and extremely strong dense fog are formed, it is not easy to dissipate in a short time. The generation time of fog is mainly from night to sunrise, and the disapperance time is mainly after sunrise.