Abstract: The at-rest earth pressure coefficient K₀ is a basic mechanical parameter of soils. So studying K₀ of coarse-grained soils is of important theoretical value and practical significance in geotechnical engineering. At present, there are few apparatuses and methods applicable for measuring K₀ of coarse-grained soils. Therefore, an accurate and reliable empirical formula for K₀ has a strong application in the actual earth-rockfill dams. For obtaining the reliable estimation formula for K₀ of coarse-grained soils, a number of K₀ tests and CD triaxial tests for a sandy gravel and a rockfill are performed by using the specially large-size K₀ apparatus and large-size triaxial apparatus, respectively. Based on the results of K₀ tests on all specimens, the relationship between K₀ and vertical stress σ’_v for the coarse-grained soils proposed by the authors is verified. By combining the relationship and triaxial test results, an empirical formula is obtained, which can well describe the relationship between K₀ and stress state under an arbitrary consolidation condition based on the effective angle of internal friction φ′. Finally, the proposed formula is verified by using K₀ test data.