Abstract: The Heihe River Basin is the second largest inland river basin in northwest China，but at the same time，it is greatly vulnerable for its arid ecological environment. The Ejin Oasis，locating in the lower reaches of the Heihe River，Inner Mongolia，China，is a vital ecological defense of forefront of the Heihe River Basin. Considering that the Ejin Oasis was undergone great changes in recent 50 years due to the influence of human activity and climate change，this paper aims at calculating the net changes of oasis area in the adjacent sample years and dividing the changing patterns of Ejin Oasis. Taking 14 image data in recent 50 years as the data source，including KeyHole，KATE-200 and Landsat MSS/TM，the spatial distribution of the oasis in Ejin Banner was firstly extracted using object-oriented image segmentation and automatic threshold method combined with visual interpretation. Then the method to calculate net changes of oasis area was proposed，the method to divide changing patterns was found out by proposing [NACKgrid，][NRCKgrid] and [NARCKgrid] under the guidance of grid-based method and the support of GIS overlay analysis function. It turned out that the method proposed in this paper was effective and it would make it easier for us to understand the direction of the change of oasis；the changing patterns of oasis in the latest 50 years could be divided into expanding，shrinking，stable and fluctuanting by the combined utilization of [NACKgrid，][NRCKgrid] and [NARCKgrid；]what’s more，the intensity of oasis change could be expressed by [NACKgrid.] As a result，the spatio-temporal changes are analyzed of the Ejin Oasis from 3 aspects：the scale of oasis，changing patterns and the intensity of oasis change，and the following conclusions were reached：（1） It turned out that the changes of the Ejin Oasis showed an expansion trend in the latest 50 years，except for a few intermittent periods of shrinkage.  Furthermore，the total area was increased by 87.05% from 1963 to 2012；（2） The fluctuating was the dominant spatio-temporal changing pattern with the proportion of 87.2% of the total area，and the expanding，stable and shrinking occupied 6.4%，4.3% and 2.1%，respectively；（3） The spatial difference of the intensity of oasis change is evident. The intensity of core area of the delta is the lowest compared with the whole region；however，the intensity of the fringe areas of the delta is relatively high，especially in the reclamation region in eastern edge of the delta. Finally，the conclusion could be shown that the Ejin Oasis was unstable，fragile and mutable in the latest 50 years，and it is a typical representation of terminal oasis in the inland river basin which shows high dependence on water resources，in stark contrast to midstream oasis which is dominated by irrigated agriculture.

Key words: spatial-temporal changes, grid transformation, overlay analysis, the Ejin Oasis