Climatic characteristics and changes of snow cover over the Northern Hemisphere, the Eurasian Continent, North America and Tibet Plateau were studied based on data of the Northern Hemisphere snow cover area observed by satellite remote sensing from 1966 to 2000. The result shows that the climatic changes are almost the same over such regions as the Northern Hemisphere, the Eurasian Continent and North America, and that an obvious reduction of snow cover area occurred around 1987. Nevertheless, the reduction of the snow cover area in Tibet Plateau happened around 1984. It shows that the internal annual snow cover variation in Tibet Plateau is not quite in agreement with that in other regions.