Abstract:Conventional observed data and the characteristic quantities of the atmospheric circulation were used to analyze the climate characteristics of snowfall day numbers in Ningxia and the affecting atmospheric circulation during the period of 1961 to 2010 by the methods of the statistic analysis, correlation analysis， and maximum entropy spectrum. The results have shown 〖JP2〗that the snowfall day numbers of each grade occurring in Ningxia have two extreme values which appear in spring and autumn. In winter， the heavier the snowfall, the lower the frequency. The geographical distribution of snowfall day numbers in different seasons is relatively consistent and increases obviously from north to south in Ningxia. High frequency centers have a strong correlation with terrain features. The frequency of non sustained 1 d snowfall is higher, and the lasted time decreases with the increasing of snowfall grades. The total day numbers of snowfall have decreased, the contributions of light snow, heavy snow and snowstorms have reduced， however, moderate snow has the opposite trend. Different grades of snowfall have different variations of short, medium and long period. Polar vortex in the Northern Hemisphere, index of the Tibetan Plateau, European Atlantic pattern and Eurasian circulation (Asia circulation) are the main atmospheric circulation systems influencing snowfall day numbers in Ningxia. The characteristic quantities of atmospheric circulation significantly correlated with snow frequency in Ningxia are season variational, so are the characteristics of atmospheric circulation. However, the affecting mechanism is the same, supplying the cold air and water vapor.