Abstract：Tiger Leaping Gorge river reach is in the middle of Jinsha River. It has the topographic and geological conditions for construction of a leading reservoir，and the development benefit is significant. The riverbed is covered by a deep layer with the maximum depth of 250 m. The technical difficulty of constructing high dams and large reservoirs on the deep layer is great. So the research of bed cover and exploration of the feasibility of constructing high dams on the deep cover has great significance for dam site selection. Through a large number of geological survey，exploration，geotechnical test and other investigation results，the profound causes of deep cover are revealed，namely，affected by the new tectonic movement，this area vertically moved evidently and formed the well-known ancient Longpan Basin in the northwest region of Yunnan Province；the Yulong Mountain on the east side of this area has been uplifting constantly since the middle Pleistocene，the Longpan basin has been continuing to accept deposits，nowadays the river bed eventually forms a deep cover. There are eight typical alternative dam sites in this reach，the river bed deposits of two of the dam sites which are located in the upper and the lower narrows of the great canyon reach respectively are relatively shallow(thickness of 40 to 50 m)；the dam foundation should be easier to be dealt with. The river bed deposits of the Shigu，Hongyan and Shangjiang dam sites in the upper reach are the deepest(thickness of 172 to 250 m) according to the current dam construction technology. These dams can only be located on the river bed，the lowest height of these dams should be 250 m；and the technology of building high earth-rockfill dams on these sites will meet or ever exceed the present technology. The depths of the river bed deposits of Longpan，Tacheng and Qizong dam sites are almost the same(about 100 m)；there are two schemes，disposal the deposits entirely or utilization of the deposits，the construction technology of any of these schemes will meet or ever exceed the top grade technology and the technology of damming should be studied. In addition，the study of the development history of the Jinsha River valley，as well as similar projects in future site selection are important scientific and reference values.
