Abstract: The availability and excavation depth of dam foundation rock, which are of important research issues in the stage of technologically design and detailed constructional drawing, are related to the feasibility, rationality and economy of hydropower projects. Based on mechanical properties of different lithologies and their combinations, such as rock thickness, RQD value, wave velocity and large-scale in-situ deformation tests, we study the structural features and quality standards of complex layered foundation. Based on the wave velocity of rock, we established an evaluation model that could forecast structure, quality and deformation parameters of rock mass. Besides, we have also determined the availability standards of complex layered rock and conducted a research to optimize the depth of excavation. The results show that for the entire dam base rock mass of which sandstone accounting for about 60%, slightly fresh or older complex layered sand-slate are characterized as hard rock; the level effect of rock disappears basically and its integrity is greatly improved. The wave velocity of rock is well corresponded to its structure, quality and deformation parameters. Based on the wave velocity of rock, we propose the availability standards of structural foundation rock. By these measures, the excavation depth of the riverbed structural foundation is reduced by 10 meters, which reduces excavation volume of rock foundation and quantity of concrete pouring and shortens the construction period.