The East Himalaya-Hengduan Mountains in the southeastern part of the Qinghai-Tibetan Plateau is a global biodiversity hotspot, but little has been reported on the botanical diversity and ecological niche characteristics of forest community in this region. We collected and compiled a list of s arborescent plants distributed and their family characteristics in the southeastern Qinghai-Tibet Plateau, and analysed the ecological niche characteristics of the major dominant species as well as the factors influencing the diversity of the forest communities. In our study, the "Levins" method was used to calculate the niche width and niche overlap value of dominant species; subsequently, the interspecific connectivity was analysed using the variance ratio method, χ² test, Association coefficient and Ochiai index; and, finally, the rate of explanation of plant diversity by each environmental factor was calculated using the variance decomposition method. The results of the study showed that: (1) the forest community in the East Himalaya-Hengduan Mountains consisted of 119 species in 42 families and 71 genera, and the species composition was mainly dominated by Pinaceae (17 species), Rhododendron (10 species), Betulaceae (9 species), Sapindaceae (8 species), and Camphoraceae (6 species); (2) the overlap of ecological niches of all plants in this region was low (mean 0.027) and ecological niches overlap values of most species pairs with were zero, which indicated that the forest community was little competition and in a relatively stable state; (3) The top 10 species in terms of niche width were, in order: Abies fabri, Rhododendron simsii, Tsuga dumosa, Picea likiangensis, Larix gmelinii, Quercus guyavifolia, Quercus semecarpifolia, Sorbus pohuashanensis, Lithocarpus glaber, and Pinus yunnanensis, and 10 species dominate the forest community; (4) the results of the inter-species associations show that the variance ratio is greater than 1, indicating that there is a strong positive association between species in the forest community, and that the different ecological niches occupied by each species in the community make rational use of various resources. (5) the mean annual temperature and slope direction were considered to be the two most critical environmental factors that affected plant diversity in the region; (6) the communities have the highest community plant diversity in intervals with mean annual temperatures of 7-11℃ and in terrain with semi-sunny slopes.