The relationship between variation and meteorological condition of atmospheric pollution in the Lanzhou City is analyzed for the period of 1961—2001 by using the observational data of smoke days. The results show that the pollution days are about 119—201 in 1961—1984,serious pollution is in 1985—1988,the mean annual pollution days are 224,obvious improvement is in 1996—2002,and the mean annual pollution days are 66. In a year,the main polluting periods are January and from November to December,and the rate of pollution days is 49 percent. In pollution days,the visibility has distinct daily variation,the shortest distance of visibility and the most serious pollution phase are from 11:00 to 14:00.