Abstract: In order to study the dormancy mechanism of Acerpseudo-sieboldianum seeds, seed permeability and inhibitory activity of endogensic inhibitory substances of Acerpseudo-sieboldianum were investigated in this paper.The water permeability between intact seed and piercing naked seed were compared,and the inhibitory activities of the methanol extracts from the pericarp,seed coat and embryo of Acerpseudo-sieboldianum against seed germination and seedling growth of wheat were also studied. The results showed that the permeability of the seed coat was good. The different concentration of methanol extracts from different parts of seeds had an inhibiting effect on plant height, fresh seedling weight ,root length and fresh root weight of wheat，which decreased the content of chlorophyll content and the activity of α-amylase and inhibited in metabolizing of the starch and soluble sugar. As the concentration increased,the inhibition enhanced.In the same concentrations, the extracts from the seed embryo could inhibit wheat germination and growth at higher level than that from the pericarp and the seed coat. In concluded,the permeability of the seed coat to water was not the main cause of seed dormancy of Acerpseudo-sieboldianum.The inhibitors were distributed in all fractions of the seeds,mainly embryo.It might be the main reason of Acerpseudo-sieboldianum long period dormancy.