Abstract: Bi-kou Dam, the highest earth and rockfill dam in China, and its two concrete cutoffs, one of which is the highest and the other is the widest, have been performing satisfactorily even since it impounded seven years, Using the modified Duncan Model, stress and displacement fields and their changesin construction, reservoir filling and steady seepage cases were analyzed with nonlinear finite element method. It conformed with operating observation data of cutoff and the safety of dam is proved. It is suggested that, when high earth and rockfill dams are designed,it should be paid attention to loading transfer in embankment and the concrete cutoff is compression support near critical condition.