Abstract: Land desertification, which is also the key factor restricting the development of Beijing, has become one of the mostserious ecological enviro nmental problems in the capital.As a result, it is urgent to study the transformation trends and formation causes of the land desertification for guaranteeing the ecological security and improving the ecological environment quality in Beijing.SPOT5 data (including panchromatic and multibands) of Beijing area in April 2007 were acqui red.The land desertification in the piedmont plain of Beijing was recognized and ex tracted with three ty pes of data (vegetation coverage, soil type and land use) from above remote sensing data.According to the ex tracted information, the desert ification status and dynamic characteristics were analyzed and evaluated with the support of RS technology.Then the formation causes of desertification were discussed combined with multiple statistical data such as meteorological information, hy drological information and soon.The resultshows that with the double effect s of nature and human beings, Yongding River, Chaobai River, Dasha River, Kangzhuang, Nankou and thei r surrounding areas are the principal distributing areas of the desertification land in Beijing.They are all f ixed sand areas that mainly contain mild and moderate desertificatio n.By comparing the result data of the land desertification among the years of 1999, 2004 and 2007, it is found that the total area of the desertification land has the trend of decrease.The area of the desertification land in each county in the suburb is reduced except Yanqing.It proves that the action of preventing and controlling the land desertification has obtained prominent effect.However, the phenomenon of destroying at the same time of improving st ill exists in some areas.Combating the land desertification still has a lo ng way to go.

Key words: land desertification, remote sensing, transformation trends, formation causes