Abstract: Based on their own research work lasting over 20 years and taking into account the seepage characteristics of the fractured rock masses and the complicated seepage prevention and drainage measures in arch dam foundations, the authors presented the main concepts and concrete techniques for strictly refined solution to 3D seepage problems in arch dam foundations with finite element method in detail. For the propose, many concepts and techniques are introduced, such as the procedure of nodal virtual flux, drainage substructure of drainage holes, transformation of type of seepage boundaries, exit flowing drainage hole, overflowing drainage hole, switch of seepage, real seepage domain, virtual seepage domain, real element, virtual element, transition element, continuous model, discontinuous model, and hybrid model. These are theoretically strict and have been widely and successfully used in practice for many years. Finally, as an example, a 3D seepage field in the foundation of a 140 m high arch dam is calculated and analyzed.