Abstract: In order to study the effects of the tree species on the germination of corp seed in agro-forestry ecosystem, chosing the paulownia and poplar as research object, the leach liquor from paulownia and poplar leaves was extracted through the way of whipping and liquation. The leaves aqueous extracts were used to study allelopathic effects on the germination of wheat, corn and soybean. The results showed that: (1)it obviously produced inhibition on germination rate of soybean once the density of paulownia and poplar leaves aqueous extracts to the point of 50mg/mL; when the density of poplar leaves aqueous extracts to 10 mg/mL and the density of paulownia leaves aqueous extracts over 20 mg/mL, it caused the obviously inhibition on germination rate of wheat and corn. (2)the allelopathic effects of poplar leaves aqueous extracts on the three kinds of crops (RI=15.147)were more than paulownia(RI=13.973); (3) the allelopathic inhibitory effects of poplar and paulownia leaves aqueous extracts were ranked as: wheat>corn>soybean. With the increasing of density of poplar and paulownia leaves aqueous extracts, the allelopathic inhibitory effects become more and more powerful and the germination rate of crops get lower.