Abstract: 【 Objective 】 This project aims to reveal the causes and types of walnut seed dormancy.The present research was carried out to investigate causal factors of the walnut seed dormancy and types.【 Method 】The walnut seeds were treated sand stratification in short period of moist low temperature sand stratification, soaked in external gibberellic acid (GA₃) , water soak treatment and water soak treatment with sunlight exposure treatment to observes seed germination percentage,germination index,germination potential. After that, the water soluble germination inhibitor in walnut seed shell was extracted and detected by bioassay. and bioassay of walnut endocarp soaking solution.【 Result 】The results showed that both moist low temperature in short period of sand stratification and GA₃ treatment did not show any significant difference compared with CK(|U|≤1.96). Both soaked (15 days) and additional sun exposure for 2h after soaking (15 days) increased the percentage of seed germination,germination index as well as the germination potential with a significant differences compared with CK (|U|≥2.58); The bioassay experiment showed that walnut endocarp contained certain amount of soluble germination inhibitory substance, compared with the control, and at the level of 1.5 g/ml (dry weight) concentration, the germination rate, root and shoot growth rate of wheat seeds were 26%, 6% and 5% of those of CK, respectively.【 Conclusion 】Comprehensive analysis showed that, the ratio of endogenous GA₃/ABA in walnut seeds might regulate its dormancy, and water soluble inhibitory substances with the mechanical hindrance of seed shell are the dominant factors to regulate dormancy. In conclusion, the project confirms that the dormancy of walnut seeds belongs to physiological dormancy type and mechanical obstacle dormancy type.