Abstract：Abstract：Based on the principle of composite element method，a new algorithm for the three-dimensional seepage problem in discontinuous rock masses is presented. The three leading features of this algorithm are as follows：(1) discontinuities segments such as faults and joints are contained in the composite elements，thus the mesh generation of discontinuous rock masses will not be restricted by the number，position and orientation of the discontinuities and can be considerably simplified. The quantity of mesh can be easily controlled；and the shape of mesh can be improved correspondingly；(2) being dissected by the discontinuities，the composite elements may contain sub-elements of arbitrary shape. The hydraulic potential in sub-elements are interpolated from their corresponding mapping nodal hydraulic potential，respectively. With the solved mapping nodal hydraulic potential，the velocity，flow rate in each sub-element can be calculated；and those in discontinuities segments are calculated from the two sets of mapping nodal hydraulic potential of their neighboring sub-elements；(3) in composite element method，the solving procedure of the mapping nodal hydraulic potential is similar to that in conventional finite element method，and the elements containing no discontinuities are degenerated to conventional finite elements automatically. Thus the programs for composite element algorithm can be incorporated into the conventional finite element analysis procedure with intrinsic coherence. The comparative study between the composite element method and the conventional finite element method for seepage problem has been implemented with two simple models and a gravity dam example，respectively；and the validity and effectiveness of this new algorithm are verified by the given examples.
