Abstract: Taking Linze County in the middle reaches of Heihe River as example,5 periods Landsat remote sensing images including MSS (1977),TM (1986,1993,2002) and ETM+ (2012) were used to extract the spatial-temporal pattern change of oasis-desertification in this region,combined with the feature of the natural landscape and oasis initial scope,Linze County was divided into 4 sub-regions (Ⅰ,Ⅱ,Ⅲ,Ⅳ) from north to south for comparison research. After that,we using the land use dynamic index and spatial-temporal variation index model to study the spatial-temporal pattern change processes of oasis-desertification land and their interactions in different regions,and the results showed that: ① Oasis-desertification land change behaved as oasis expansion and desert retreat from local to overall region,but the characteristic of oasis-desert land change and the degree of desertification in different regions was disparate. Regional Ⅰ and are Ⅱ dominated by extremely severe desertification land,and they changed fast in 1986-1993 and 2002-2012 respectively,region Ⅲ changed fast in 1986-2002,and its degree of desertification was getting worse,from light desertification to severe and extremely severe desertification land,while region Ⅳ only distributed oasis and haven't changed much. ② The spatial variation of oasis-desertification land from north to south were oasis-desertification ecotone change,spatial imbalance change in oasis fringe and internal of desertification land,fragmentation of desertification land respectively,the changes in region Ⅳ is mainly city expansion in the north.③ The human factors were the dominant factor of oasis-desertification land change in Linze County,institution and policies become the root causes of the periodic change,while the personal wishes and the responses were the direct cause,the main reason of the regional differences was the natural conditions and immigration. ④ Oasis-desertification land change can be divided into three stages: the livelihoods drive,the economic drive and the ecological-economic drive,in the context of the ecological resource pressures,the future development of oasis needs to adjust to local conditions and pay more attention to reversing of desertification and expansion of salinization.

Key words: oasis, desertification, spatial-temporal change, contrastive analysis, Linze County, middle reaches of Heihe River