Abstract: Integrating with the design and construction of the high earth and rockfill dam on Shitouhe River, the experiments on shear strength of big grain-size sandy-gravel, the cover material of the dam, were made with a 2×2×1m large-scale double-box type direct shear apparatus. According to the analysis of the method and results of the test, the new criteria for selection of designed values of sandy gravels is recommended. By adopting it, the cross-sectional area of the dam may be greatly reduced as compared with the original design.