Abstract: The reliability of seepage prevention system is a key problem for high earth-rockfill dam located in a foundation of large overburden depth. The conjoining area of the anti-seepage soil body and the concrete diaphragm wall is a key part against seepage induced failure. According to the characteristics of the seepage prevention system of the Pubugou earth-rockfill dam, a finite element method (FEM) is applied to analyze the seepage flow of the whole dam. The analysis results show that the appurtenant impervious wall taking 40% water head is suitable, and that the seepage gradient in the conjoined area is inhomogeneous around the concrete structure. The seepage gradient at the top of the structure is much bigger than that at the outlet of the earth core wall base. The analysis results can be taken as the references for similar projects (works) in the future.