Abstract: Eupatorium adenophorum is a worldwide noxious weed with a very high invasive ability.An interspecific competition experiment was conducted in a greenhouse to observe growth of E.adenophorum affected by interspecific competition,and to interpret the relationship between the interspecific competition and population density.Result indicate that interspecific competition reduced average plant height and lamina number,root sprout number,and biomass of individual E.adenophorum as planting density increased from 25 to 700 plants·m^-2.The lg biomass was highly negatively correlated with the lg density with r²=0.99 and gradient=-5/6.Meanwhile,differences between plants of various size hierarchy intensified as the plant density increased,indicating that different plant individuals were exposed to different density stress within the community.When the planting density was very high,E.adenophorum plants would control formation of root sprouts,or even let them die so as to reduce their consumption of resources for survival in the habitat.This suggested that vicarious species should be planted and germinated earlier than E.adenophorum once applying substitution method,by which E.adenophrum could be suppressed by the planted vicarious neighbors.