Intraspecific and interspecific competitions are important relationships of plants. We analyzed competition intensity using field data for 95 Japanese yew (Taxus cuspidata) target trees and 980 individuals of competing species by using the competition index (CI) in Muling Nature Reserve of eastern Heilongjiang Province. The intraspecific competition of Japanese yew population was weak, accounting for 4 percent of total competition, and the main stress to the Japanese yew population came from interspecific competition, which accounted for 96 percent of the total. The main competitors were the dominant species of the zonal vegetation types，including Abies nephrolepis, Tilia amurensis, Acer mono and Pinus koraiensis. The competition intensity of Japanese yew declined with increasing DBH, and the stress was more intense for trees less than 20 cm in DBH. The relationship between competition intensity and DBH of target trees followed the equation CI=AD-B.