Abstract: Based on the investigations of 45 objective trees and 205 competitive trees of Taxus yunnanensis population in the Jinsha River Basin of northwest Yunnan Province and by using Hegyi’s single-tree competition index model, this paper analyzed the intra- and interspecific competition intensities of endangered plant T. yunnanensis. The intraspecific competition intensity of  T. yunnanensis decreased with its increasing diameter at breast height (DBH), presenting a partial peak curve, whereas the intraspecific competition intensity of  T. yunnanensis was the highest at its DBH 5-10 cm, and then showed a decreasing trend with the increase of the DBH. The interspecific competition intensity (133.61) of  T. yunnanensis was significantly higher than the intraspecific competition intensity (76.88), indicating that the competitive stress of the T. yunnanensis population was mainly come from interspecific competition. The intra- and interspecific competition intensities of T. yunnanensis were larger than those of the local common tree species Tsuga forrestii, Betula albosinensis, Populus szechuanica, Quercus aquifolioides, and Aralia thomsonii var. glabrescens, with the competition indices being >5. The competition index of T. yunnanensis with the objective trees in the whole forest stand was significantly negatively correlated with the DBH of the objective trees, and nearly conformed to power function (CI=aD^b). The larger the DBH of the objective trees, the smaller the competitive stress of the T. yunnanensis population.