Abstract: The paper aims to explore the reason that Eupatorium adenophorum is more under Pinus massoniana forests and less under Quercus glauca forests in field. Taking seed germination parameters (germination rate, bud length, root length and fresh weight) and the seedling growth parameters (plant height, maximum leaf area) as evaluation index, the authors studied the effects of the litter cover and water extract on the seed germination of Eupatorium adenophorum and the growth of its seedlings on the basis of indoor potted tests and field simulation. The results showed that: (1) the influence of the cover under Pinus massoniana forests on the seed germination and the growth of Eupatorium adenophorum seedlings was greater than that of uncover, but with no significant difference; (2) the cover under Quercus glauca forests seriously inhibited the seed germination and the growth of Eupatorium adenophorum seedlings; uncover had no influence on the germination rate but obviously inhibited the growth of the seedlings; (3) the water extract of Pinus massoniana had almost no influence on the seed germination and seedling growth, and the water extract of Quercus glauca intensely inhibited the seed germination and seedling growth except the seed germination rate. The main reasons for the significant density differences of Eupatorium adenophorum under Pinus massoniana forests and Quercus glauca forests are: the needle litter cover of the former can keep soil moisture and permeability and litter decomposition provides soil nutrients suitable for the growth of Eupatorium adenophorum; the broadleaved litter cover of the latter cannot keep permeability and litter decomposition releases allelochemicals that inhibit the growth of Eupatorium adenophorum.