The engineering properties of weak intercalations are not only related to the environmental conditions, such as ground stress, ground water, etc., but also to their genesis, granularity composition and mineral composition. Under the same genesis, grain composition and material composition, the relationship between shear strength and water content, properties index (W/Wp), dry density is analyzed by experimental study, and the related equations are established. The results reveal that shear strength increases with the decrease of water content and properties index and the increase of dry density. Therefore, to select strength parameters of weak intercalation in the specific engineering, the factors, such as water content, grain composition, clay mineral composition, and ground stress, should be taken into account. In addition, shortcomings of the strength parameters of weak intercalation that only relies on the quantify index of granularity composition in Design Specification for concrete gravity dams is discussed.