This paper discusses the methods used for thematic information extraction in desert area with TM/ETM as the main data resource. The water body was extracted by combining density slicing of TM 5 or TM 7 with the terrain mask produced by DEM. NDVI was used to extract vegetation information, and desertification land and salification land information was extracted by the SAM classification method. Confusion matrix shows that the classification precision is 86.2%. The classification results of desertification land and salification land in different years were input into GIS to extract changing information by using spatial analysis. It is shown that from 1994 to 2000, desertification and salification land increased obviously, whereas from 2000 to 2002, desertification and salification land changed only insignificantly. Considering that the study area is located in an arid desert environment short of human activities, and that the main factors affecting landscape change are climate and hydrological conditions which may not change remarkably in a short period, the suitable monitoring period should be five years or so.