In the calculation of seepage or consolidation, if there is a large difference in seepage coefficient of two adjacent materials, the release point, as well as the phreatic line, should be determined by iterations. However, if we set interface elements between two materials, reasonable results of release point can be captured without iterations. In this paper, two seepage cases are investigated, and the composite seepage coefficient of the elements, which are intersected by the phreatic line, is calculated with the Monte Carlo integration method. Two interface elements are set between two materials with great difference in seepage coefficient. The hydraulic relationship between two materials is built based on the seepage matrices of the interface elements, while the location of the phreatic line is then calculated by iterations. Choosing a thin thickness for the interface element(e. g. , 1/4 of the thickness of the adjacent element)could localize the error of calculation, which has little impact to the whole area at the same time. By choosing an appropriate seepage coefficient or permeability rate of the interface element, results close to those obtained through the traditional methods can be acquired, which shows the applicability of the proposed method.