Abstract: Mechanism of Castanea mollissima cv.'Yanshanhong' seed dormancy was studied by exploring the testa effect, embryo form and inclusion variation.The following conclusions were drawn as: The immaturity of embryo should be the major factor to cause the seed dormancy.Both the embryo length and the length ratio of cotyledon and the radicle increased along with prolonging the sand stratification duration.The testa constrained the seed germination to a certain degree, for the germination percentage increased when the seeds were peeled off partially or completely.It was deduced from the experiment that P-coumaric acid could be another factor to inhibit the seed germination, since its concentration dropped obviously along the course of sand stratification.There was no clear relationship between the GA₃/ABA ratio in the seed kernel and the germination.The inhibiting effect of P-Coumaric acid was proven by treating Castanea mollissima cv.'Yanshanhong' seeds with P-coumaric acid with varied concentrations.