Abstract: Typical plots were established in Daxing’an mountain,Xiaoxing’an mountain,and ecotone of the Notheast of China Plant species composition and vertical structure of different distribution regions were studied in Daxing’an Mountain, Xiaoxing’an Mountain and ecotone using species richness, Simpson diversity index, Shannon-Wiener index and evenness index. Meanwhile, the biodiversity and evenness index of the same community in different regions and different life-forms were compared and analysed.The results indicated:There is significant characteristic of transition between Daxing’an Mountain and Xiaoxing’an Mountain. Theopencedrymion dominates Xiaoxing’an Mountain and ecotone,conifer-conifer forest dominates Daxing’an Mountain;The species diversity indexes of three regions are Xiaoxing’an Mountain＞econtone＞Daxing’an Mountain;The species diversity of different life-forms in different plant regions are herb layer＞shrub layer＞tree layer. Species diversity was significant different in tree layer, but not found in shrubs layer and herb layer.

Key words: Daxing&rsquo, an Mountain, Xiaoxing&rsquo, an Mountain, ecotone, species diversity