Wudongde Hydropower Station lies on the Jingsha River

which is located at the upstream of the Yangtze River. The earth rockfill cofferdam is 74m high; the boulder overburden layer of river bed is 70m deep; and the water head difference is 151m. A foundation pit with the depth of 70 m is planned to excavated at the toe of the cofferdam at the downstream side

and concrete wall( 86m high) with geomembrane on the top

the geomembrane has the depth of 43m. The stress and deformation characters of the cofferdam are analyzed by the nonlinear FEM. The processes of construction

the upstream water level

and the excavation in downstream side were modeled. The interface between filling material and the cut-off wall is modeled by Goodman element without thickness. Results of stress and deformation analysis indicate that the design scheme is feasible.Furthermore

the influences of the paramerters of the overburden layer

the influences of filling materials

and the influences of the material

the thickness and the bottom sediment of the cut-off wall are studied. Some suggestions obtained from analysis are presented for the design scheme.