Abstract: Biodiversity is an important consideration in the monitoring and assessment of the ecological stability of rangelands in Tibet. Climate warming and grazing disturbance both threaten the stability of the Tibetan rangelands; hence, research into species succession, transition patterns and species diversity is important for the protection and utilization of grasslands in the region. A field survey was carried out to measure the community species composition and the species change along an altitudinal gradient in the Bailang village valley, Linzhou County in the Lhasa River Basin. Three conventional sampling methods, random square quadrats, repeat sampling lines and the Modified-Whittaker plots, were compared in this study. Key results were: (1) All three sampling methods indicated that α-diversity initially increased and then decreased with increasing altitude, though the line transect method using three 50 m transects detected more species than the other two methods. (2) The Sorensen similarity index and the Bray-Curtis index of β-diversity decreased with increasing altitude. (3) The intercept c and slope z of the relationship between species and sampling area showed unimodal patterns with increasing altitude as also did species richness. (4) In order to cover 80% of local plant species, the minimum sampling area should be up to 100 m². Future research should focus on the factors determining biodiversity distribution and community assembly in response to climate change and grazing disturbance.