Abstract: In order to determine the cuttingout range of seepage model which must meet pr ecise requirements of seepage analysis for twostratified foundation in the lev ee engineering,a relation expression between length(L) representing the mode l cuttingout range and computed error (p) of seepage discharge is derived on the basis of seepage theoretical solution for twostratified foundation in t he levee engineering,and, by this formula,a model cuttingout range which can s at isfy seepage analysis precision for engineering application may be determined.Th e effective length(Le) of model is equal to 3/A.