Abstract: The germination test of Pinus yunnanensis seeds treated by the ether and ethanol extraction solution with three concentrations of 800mg/kg, 400mg/kg and 150mg/kg from the fresh branch, fresh leaves, bark, root and litter of Alnus nepalensis was conducted to observe the allelopathic effect between the two tree species. The results showed that the extraction of A. nepalensis in higher concentration had negative effect on germination percentage of Pinus yunnanensis seeds, germination potential and dry seedling weight. The negative effect was weakened with the lowering of the extraction concentration, and then the positive effect became stronger. In terms of the positive effect of the extraction prepared from different Alnus nepalensis organs, the extraction of fresh branch and litter was higher than other organs. Whereas the bark of A. nepalensis contained more allelopathic substance with negative effects on germination percentage, germination potential and the dry seedling weight of Pinus yunnanensis. Among the three criteria tested, the dry seedling weight was most sensitive to the allelopathic effect, followed by germination potential and germination percentage. It was proposed that the litter of Alnus nepalensis should be kept for natural decomposition inside the mixed forest and the proportion of the two tree species should be well controlled in order to stimulate the natural regeneration and growth of Pinus yunnanensis.