Abstract: Desertification is a global problem that threatens the survival and development of human being.China is seriously impacted by desertification.Based on the records of historical literature and the research results of modern scholars,this paper sorts out the evolution process of China's sandy desertification in three historical periods,namely,the 1st period from Qin and Han Dynasties to the Wei Jin and Southern and Northern Dynasties,the 2^nd period from the Sui and Tang Dynasties to the Song and Yuan Dynasties,and the 3^rd period of the Ming and Qing dynasties.The research shows that the coverage rate of China's desert was not more than 10% before four millennia,especially in the Spring and Autumn period and Warring States period (770 BC-221 BC),the climate was warm and humid,and the ecological environment in most parts of North China was in balance.During the 1st period,due to the increase of the population in the northwest of China,the large-scale reclamation and wood cutting,the natural ecological environment had been destroyed,resulting in the decrease of the surface vegetation and the desertification of the soil.Therefore,in this period sandy desertification in China was mainly concentrated in the western region of China,such as Ordos Plateau,Hexi Corridor and Xinjiang region.During the 2^nd period,sandy desertification was extended to the northeast of China,such as Hulunbuir Sandy Land,Horqin Sandy Land and so on.Meanwhile,the government vigorously developed Hexi and western regions in the early Tang Dynasty,and the ancient cities of the southern Tarim Basin in Xinjiang were abandoned or deserted along with the time.At the same time,the desertification in the northern Ordos Plateau was becoming more and more serious,and the Mu Us Sandy Land and the Hobq Desert were gradually formed.During the 3^rd period,through building the Great Wall and prohibition policy by the government,the wasteland reclamation of border area was controlled.However,under the population pressure,agricultural reclamation in northern frontier was developed rapidly in the late Ming Dynasty and late Qing Dynasty.This phenomenon accelerated desertification in Ordos Plateau and Horqin Sandy Land.In a long period,changes in climate and natural conditions have played a fundamental role in desertification process.In a short period,human activities have an important impact on desertification in some areas,especially agricultural reclamation and wood cutting destroyed the vegetation of the surface and caused the degradation of the vegetation communities.Therefore,for thousands of years,the climate change and human activities,especially the unreasonable land use methods,such as indiscriminate reclamation,grazing and firewood chopping and collecting,have caused the desertification in the arid and semi-arid areas of the north of China to become more and more serious.

Key words: ancient China, sandy desertification, Hexi Corridor, Ordos Plateau, Horqin Sandy Land