As one of the most noxious plant invaders in China, Ageratina adenophora (Sprengel) R. M. King & H. Robinson not only severely threatens the biodiversity security and but also leads to huge economic costs to the country. To simulate the natural environments, A. adenophora was grown together with 4 receiver plants, Chromolaena odorata（L.）R. M. King & H. Robinson, Bidens pilosa L. Ageratum conyzoides L. and Gynura sp. respectively, to set-up four types of man-made communities. In half of the communities activated carbon was used to absorb allelochemicals, and in turn to eliminate allelopathy between plants. In this way allelopathy and irradiance acclimation characteristics of A. adenophora were studied separately, and their relationships with invasiveness were discussed. 
After growing with A. adenophora for more than three months, C. odorata, A. conyzoides, B. pilosa and Gynura sp. in communities with activated carbon did not show any significant difference with the plants of the same species in communities without activated carbon in all of the morphological and physiological parameters measured in this study. These results indicated that in the early phase of invasion A. adenophora did not affect its neighbors by allelopathy. In contrast, A. adenophora were affected in few traits by the receiver’s allelochemicals. C. odorata reduced its basal diameter; B. pilosa reduced its leaf numbers but increased its height; Gynura sp. reduced its ascorbate peroxidase activity. At early invasion stage, A. adenophora seedlings were located in the lower layer in all of the four types of microcosms constructed in this study, so irradiance around them was weak. A. adenophora could adequately acclimate to the light environments in the communities. Twelve parameters measured in this study were significantly associated (p<0.05) with the light intensities that A. adenophora encountered in the communities. A. adenophora could tolerate weak light environments. With the increase of light intensity A. adenophora’s maximum net photosynthetic rate, activity of superoxide dismutase, the ratio of chlorophyll a to b, total plant biomass, total leaf area, basal diameter, numbers of leaves and branches increased, while its specific leaf area and specific stem length decreased. These morphological and physiological changes made it possible for A. adenophora to keep leaves energy balance and to shade-out its neighbors in high light environment. We attributed A. adenophora’s invasiveness to its remarkable light acclimation ability, especially to its shading-out effect on native plant species in high light environment.