The source region of the Yellow River is located in the northeast of Qinghai—Tibet Plateau,and its eco-environment becomes very fragile for the especial geographic location in recent years.Influenced by natural factors together with human being factor in these years,eco-environment in the region degrades very quickly,and desertification is the major problem.Supported by GIS and RS,as well as field investigation and indoor analyses,an eco-environmental information system in the region is worked out.A classification is performed,multi-source data are gathered,and the present status,classification and spatial distribution of land desertification in the whole region are showed based on the data obtained from field investigations and Landsat TM images(4,3 and 2 bands) of September 2005.The result indicates that the desertified land in the study area is mainly concentrated in Gonghe Basin and upland plain area.The total area of desertification land is 13434.8 km2,14.65% of the entire land in the aim region.There are many reasons responsible for the desertification process,of which the main reasons are the geological environmental evolution,regional climate change,and human irrational activities.