On the basis of field investigations, the timberline range of Beitai, the Xiaowutai Mountains was carved up, and the changes in the makeup and diversity of plants with the altitude were discussed. The results showed that the timberline with gradual changes in the northern slope of Beitai ranged from 2620-2800 m. In timberline, herbaceous plants were rich, and the diversity was higher than that in coniferous forest and sub-alpine meadow zones. The turnover rates of species were gradually hoisting from the centre of timberline to sub-alpine meadow and forest zones, and highest at the edge of timberline. Betula, Picea meyreri and Larix principis-ruprechtii species were the ecological indicator for research on environmental changes. Climate indication significance of these arbor species distributed in and near the timberline was also discussed.