Abstract: The impacts of desertified land change (DLC) during the construction of QinghaiTibet Railway of China from Golmud to Lhasa have given rise to important research significance.Based on the Landsat image,Google Earth image and the meteorological data about Co Nag Lake region along QinghaiTibet Railway,this study uses RS and GIS technologies and conducts fieldwork to establish interpretation signs and to construct a classification & grading system for the DLC in the study area,and then employs visual interpretation method to extract the DLC information in 2001,2008 and 2015 respectively.The spatiotemporal evolution of the DLC over the last 15 years is analyzed.The results show as follows: (1) In 2015,the desertified land was mainly sandy land but the area of sandy gravel land was relatively small in study area.The area of desertified land was increased by 2.21 km² from 2001 to 2008 yet the degree of land desertification showed a declining trend.The desertified land was decreased by 8.9 km² from 2008 to 2015 and the declining degree of land desertification continued. (2) From 2001 to 2008,the increase in desertified land area was related to the increase in the number of livestock such as yak and sheep.The decline of land desertification was mainly due to the increase of annual mean temperature and the decrease in annual mean wind speed.From 2008 to 2015,the decrease of desertified land and the alleviation of the degree of land desertification were resulted from the gradual decrease in the number of livestock and the implementation of ecological restoration projects by the local government.Hence,human activities played an important role in the decline of land desertification in the 15 years. (3) The construction of the Qinghai-Tibet railway generated a disturbance to the ecological environment in the study area.The scope of influence by railway is about 2 km.While the engineering measurements of controlling land desertification along the railway lines played an important role in alleviating the degree of land desertification.In short,the discussion of the factors including the impacts of railway construction on DLC can provide some scientific basis for the prevention of land desertification and for the rehabilitation of ecological environment.

Key words: QinghaiTibet Railway, Co Nag Lake, desertification, natural factors, human factors