The alpine timberline (AT) is an important ecotone of mountain vegetation. Extensive researches have been conducting in this ecotone for its dynamic state of vegetation and sensitivity to climate change. Investigating the location and the distribution of AT in a mountain area is significant for the research of dynamic AT. With the RS data and spatial analysis techniques, it is convenient and efficient to achieve this purpose. The Helan Mountain, which is in the adjacent area of the Yinchuan Plain and the Inner Mongolia Prairie, has a representative altitudinal vegetation-belt spectrum in the arid western part of China. It is a good area for AT research. The AT positions on Helan Mountain were obtained from Landsat 8-OLI and DEM by using RS and GIS methods. The NDVI of major vegetation types and vertical distribution pattern of ATs were analyzed in this study. The results are as follows: 1) The ATs on Helan Mountain appear on the altitudes of 2 900-3 200 m.a.s.l, which is revealed by the vertical distribution pattern of the subalpine conifer forest and alpine scrub, meadow. 2) The mean elevation of AT upper borderline and lower borderline is 3 106 m.a.s.l and 3 022 m.a.s.l respectively. The mean elevations of both AT borderlines are higher on the north and east slopes than on the west and south slopes. 3) The NDVI data is an effective supplement for image classification to detect AT.