Abstract: One of the difficult technical problems for hydropower development in west China is how to take the undisturbed soil samples from the thick deposits in the river bed through boreholes and how to gained the physical and mechanical properties by the laboratory test and in-situ test. The thickness of the river deposits at the Wudongde dam site area is 52~65m.The alluvial, the colluvium and landslide mass constitute the river deposit. So the component and the structure of the river deposits show inhomogeneous Properties. The Wudongde narrow valley is apt to building the arc dam type. So the stability of the high cofferdam and the slope of the deep foundation pit are prominent engineering geological problems. For exploring the engineering characteristics of the river deposit, the advance exploring technology and the methods of the laboratory test and in-situ test were adopted. The standard penetration test was used during the drilling in order to pre-exploring the soft layer such as silt-clay, clay. In order to taking the undisturbed soil samples from the borehole, Single Rotary and Double Tube Core Barrel and The hammer Double Core Barrel With Inner Tube were developed. In order to verifying the physical and mechanical properties, the in-situ test (including the heavy dynamic penetration test, super-heavy dynamic penetration test, pressuremeter test, pumping test, acoustic prospecting and borehole TV .etc) and the laboratory test, the simulation of the soil sample gradation test were used . It is successfully solved the difficult problems of the exploration and the test in the thick river deposits and provided the reliable parameters for designing the high cofferdam and the cut slope of the deep foundation pit.