The competition relation between Eupatorium adenophorum and Artemisia annua was studied by using the multiple De Wit replacement series design method, which discussed the effects of growing character of E.adenophorum in different planting densities and mixture proportions. The results showed that the relative yield (RYg) and the relative density (RDg) were less than 1 in mixture sample area between E.adenophorum and A.annua; with the increase of the mixture proportion of A.annua,the RYg and RDg of E.adenophorum were gradually decreasing, and stem diameter, branch number and biomass were also decreasing, which implied that the competition between E.adenophorum and A.annua was severer than intraspecific competition of E.adenophorum and the population expansion of E.adenophorum was restrained when A.annua existed. With the increase of the population density under the circumstance of higher mixture proportion of A.annua, root/shoot radio of E.adenophorum had a trend of reduction，but plant height of E.adenophorum had a trend of increase, which suggested that E.adenophorum had to adopt the allocation of resources model, namely, the strategy of the ground priority growth in response to stronger pressure of competition of A.annua. Based on the above results, we should replace E.adenophorum with A.annua at the early stages of invasion to have a good effect on the control of E.adenophorum.