At present,steppe degradation is a major environmental problem in Inner Mongolia of China,resulting in desertification and reduction of steppe productivity.However,data on area, change and forecast of steppe degradation is inadequate at regional level.Steppe in the Xilin River Basin is one of the typical patterns in pastoral area of northern China,it is also one of the most important husbandry bases in Inner Mongolia and an UNESCO/MAB Biosphere Reserve.Using Landsat TM images of1985and1999,and combining with field community investi-gation,we compiled steppe vegetation maps in1985and1999of the Xilin River Basin.Further,according to the model of degradation succession of typical steppe in Inner Mongolia,we com-piled steppe degradation maps.Supported with ARC/INFO and ARC/VIEW,grid sampling on steppe degradation map was finished,the size of each grid is3km×3km.Based on steppe degra-dation index(SDI)aggregating the information of area and grade of steppe degradation developed by the authors,the SDI of each grid was calculated.The values of SDI were divided into five grades to indicate the degree of steppe degradation increase.In1999,the total area of grids where the value of SDI is3is3924km 2 ,36.67%of the total area of the Xilin River Basin;the total area of grids where the value of SDI is4and5is5049km 2 ,47.18%of the total area.Then,the translation probability matrix from1985to1999of different grade of degraded steppe was calculated.With application of Markov process,the changing trend of steppe degra-dation pattern in the Xilin River Basin was forecasted.The results showed that if no fundmental measures are taken to prevent steppe degradation in this region,the trend of degradation will continue.That is to say,the area of steppe at grades1,2and3will decrease,and that of grades4and5will increase.Up to2025,the total area of grids where the value of SDI is3is3389km 2 ,31.67%of the total area of the Xilin River Basin;the total area of grids where the value of SDI is4and5is6406km 2 ,59.86%of the total area.