Abstract: To study the reasons for dormancy of Acer triflorum, seed germination and seedlings growth of Brassica campestris in different concentrations of the methanol extract from Acer triflorum seed coats, pericarp and embryo were study in order to investigate the relationship between the restraining substraces in seed coat ,pericarp and embryo in dormancy of Acer triflorum. The results showed that with the extract concentration increased ,the inhibitory effects of Brassica campestris seed germination rate,seedling shoot elongation,stem length and simplified vigor index were gradually increased except the 30% pericarp methanol extract. In the same concentrations, the inhibitory effect of the embryo was relatively strong, the pericarp and the seed coat were relatively weak. It is concluded that the inhibitors were distributed in all fractions of the seeds,and the existence of inhibitors in components of Acer triflorum seeds is the main cause of dormancy of Acer triflorum seeds.