关键词: 大西北, 地理环境系统, 四大环境问题

Abstract: Based on point of view of geographic system, this paper puts forward a conception of Great Northwest of China, discusses the characteristics of geographic environment system and analyses land degradation such as sandy desertification，salinization, degradation of grassland and loss of water and soil. Relationship between change of paleogeographic environment and land degradation is proposed. Those fow Cypes of land degradation are characte-ristic of climatic condition becoming drier and drier since mid-Pleistocene. It is very important that the economic development of region should consider the change of paleogeographic environment and control the speed-up of land degradation.