Abstract: In order to identify whether Davidia involucrata and its associated tree species Bothrocaryum controversum affect the seed germination and seedling growth of other plants through allelopathic effects to maintain their stable associated relationship,the branches and leaves of wild D.involucrata and B.controversum in Pingwu County were used as the material source of the water extract,and the seeds of Brassica pekinensi were explored the effects of water extracts of the branches or leaves of the two species or their mixture at five concentrations（0,0.025,0.050,0.075,0.100 g·m L-1）on the seed germination and seedling growth of B.pekinensi respectively.The results showed:（1）Water extracts of branches of D.involucrata and Bothrocaryum controversum had little effect on the germination of Brassila pekinensi seeds,but seedlings growth was significantly promoted and increased with increasing concentration（P＜0.05）.（2） The water extracts of D.involucrata and Bothrocaryum controversum had significant inhibitory effects on seed germination of Brassila pekinensi（P＜0.05）,but their effects on seedling growth were different.The former showed the phenomenon of“low promotion and high inhibition”with the increase of concentration,while the latter showed the characteristic of“inhibition increase”.（3）The water extracts from different sources of branches-leaves mixtures had significant inhibitory effect on seed germination of Brassila pekinensi（P＜0.05）,and showed the characteristics of“low promotion and high inhibition”with the increase of concentration.The results demonstrated that the allelopathic effects of water extracts from branches and leaves of D.involucrata and Bothrocaryum controversum on seed germination and seedling growth of the same recipient plant were different,and different species,parts and concentrations could lead to different allelopathic intensity and direction.This phenomenon might be a long-term plant evolution and maintained the stable interspecific relationships.