Abstract: Distribution of the oasis in Gaotai County, Gansu Province was extracted by taking the 13 images in recent 50 years as the data sources, including LandsatMSS/TM, KeyHole and KATE-200. The single dynamic degree and bidirectional dynamic degree of the oasis were calculated, the relative change rates of the oasis in all the townships and towns in Gaotai County were estomated, and an overlay analysis on the vector data about distribution of the oasis in 13 periods were carried out to get the area and spatial change of the oasis in time sequence. The results showed that the oasis in Gaotai County was in expansion in recent 50 years, especially during the period from 1990 to 1993. The analyzed results of bidirectional dynamic degree revealed that the conversion between oasis and nonoasis was violent. The stable parts of the oasis were mainly distributed along the Heihe River and around the residential areas, the changeable parts of the oasis were distributed surrounding the oasis. The urban and rural areas of Luotuo Town and Nanhua Town were the main areas where the oasis was in expansion, and the frequent expansion and shrinkage of the oasis occurred mainly in Luocheng, Xinba, Heiquan townships.

Key words: oasis, dynamic degree, relative change rate, spatiotemporal change, Gaotai County, Zhangye