The seeds and seedlings of native plant species Sophora davidii were treated using an extraneous solution for 2-3 years with different concentrations of aqueous leaf extract of Eupatorium adenophorum to analyze tolerance degree and resistance mechanism of S. davidii under allelopathic effect. The result showed that the aqueous leaf extract of E. adenophorum could inhibit seed germination and seedling growth of S. davidii at high concentration. On the other hand, the aqueous leaf extract of E. adenophorum could promote seed germination and seedling growth of S. davidii at low concentration. Furthermore, a concentration of 0.5% has the strongest promoting effect, whereas when the concentration is greater than 2.0%, the inhibition effect significantly increased. Seed germination speed was more sensitive to the extract than seed germination rate. The hypocotyl is more sensitive than the radicle. With seedling growth, the ability of S. davidii to resist the allelopathic effect of E. adenophorum gradually increased. MDA content is proportional to the plant growth response; it could greatly increase rhizobium growth probability of S. davidii seedling and decrease the time of mycorrhiza formation through the treatment of the aqueous leaf extract of E. adenophorum.