Oasis-desert transition zone, an ecological buffer area, plays an important role in maintaining the energy flow, material cycle and landscape stability in oasis ecosystem. The wideness and attributes of the transition zone directly affect its function within an entire oasis ecosystem. Based on the Landsat (OLI) NDVI data of Zhangye oasis in the middle of Hexi corridor, along with field investigation, this paper divides the oasis-desert transition zone into four types including oasis with stony bare mountain, gravel desert, sandy desert, and artificial sand-fixation zone. Then, buffer analysis, focal analysis and piecewise linear trend analysis were used to study the wideness and scale-dependence effects of different transition zones. The results showed that there were two kinds of linear regression trends in the variation of the NDVI at the outside edge of the oasis boundary, and the distance from the intersection of the trend line to the oasis boundary could be determined as the transition zone wideness. The focal analysis of different scales showed that the wideness between oasis and stony bare mountain was 165-220 m, where the linear variation trend of NDVI was significant (P < 0.05). The wideness between oasis and gravel desert transition zone was about 330 m in different focal scales, where the variation trend of NDVI was extremely significant (P < 0.001). The wideness between oasis and sandy desert varied from 230 m to 290 m, where the variation trend of NDVI was also extremely significant (P < 0.001). The wideness between oasis and artificial sand fixation varied from 570 m to 580 m, where two kinds of NDVI variation trends were observed, being extremely significant only within 210-240 m (P < 0.001), but not significant (P > 0.05) beyond this range.