In a greenhouse experiment, the effects of soil microorganisms and extracts of Achnatherum inebrians on the seed germination and seedling growth of Elymus nutans were studied. The results showed that both the extracts from aboveground and belowground parts of A. inebrians significantly inhibited the germination rate, germination potential, germination index, vigor index, seedling height, root length, and fresh weight of E. nutans, but increased malondialdehyde content, catalase, peroxidase and superoxide dismutase activity of E. nutans seedlings (p < 0.05). The allelopathy of aqueous extracts of the aboveground parts of A. inebrians was stronger than that of the precipitates. Aqueous extracts of the aboveground parts of A. inebrians decreased seed germination rate, germination potential, germination index, vigor index, seedling length, root length, and seedling fresh weight by 10.