Abstract: In this paper, we utilize sand model test as the basis to study the physical and mechanical processes of unsteady seepage in homogeneous earth dams on impervious foundation. Some factors influencing the effective porosity μ are analysed. Based on the action of effective porosity μ in the unsteady seepage, it must be considered that μ changes with time in calculation.With a great deal of computations by finite element method and comprehensive analyses of the position of free surfaces, distribution of flow field and stability of upstream slope, the physical configuration of unsteady seepage in embankment dams is satisfied with eq. 4 if different values of μ in corresponding time intervals are suitably chosen.