Abstract: In order to reduce the grid dependence of traditional continuum medium seepage model and improve stability of numerical calculation, based on the continuum medium seepage model, the horizontal and vertical pores in the uniform porous media were generalized as orthogonal fracture networks by introducing the representative elementary volume, and an equivalent fracture network model for free surface seepage problems is established.The equivalent form of seepage velocity, continuity equation and boundary conditions were derived.The two dimensional seepage problem was transformed into one dimensional seepage problem of equivalent fracture network model.Combining with the continuous penalty Heaviside function, the flow velocity in wet zone was extended to the whole flow domain and the finite element formulation was presented.The validity of the equivalent fracture network model was verified by comparing it with the numerical solutions of homogeneous rectangular and trapezoidal dams.Finally, the proposed method was applied to the sensitivity analysis of the permeability coefficient of a zoned dam with clay core and sand shell.The distributions of the free surface in the clay core and the upstream and downstream sand shells were well presented and the water blocking effect of the clay core was also demonstrated.