Abstract:The competitive ability and growth characteristics of the perennial ryegrass (Lolium perenne) and the alien invasive weed (Eupatorium adenophorum) were studied by using de Wit replacement series method. The density, mixture proportion, and ryegrass-transplant time had significant effects on the aboveground biomass of E. adenophorum. The competitive ability of E. adenophorum was increased with postponing ryegrass-transplant, and planted at low density. The aboveground and belowground biomasses of L. perenne were significantly affected by density, mixture proportion, ryegrass-transplant time, and their interactions. The competitive ability of L. perenne was decreased with postponing ryegrass-transplant, and with density increasing. The results indicated that there were more interspecific competition of E. adenophorum experienced than that of L. perenne, while L. perenne had more intraspecific competition than interspecific competition when transplanted at the same with E. adenophorum, it indicated that L. perenne was a stronger competitor.