Abstract: Two-dimensional seepage flow of free-surface over cutoff wall has been solved by conformal transformation method in this paper.By introducing the hodograph plane and utilizing Schwarz-Christoffel transform,the mapping relational formula between the physical plane Z(x,y) and complex potential plane ξ(Φ,Ψ)has been deduced.The main four parameters and integrated constants also have been obtained by joint-solution method.The solution example indicates that the solution method is feasible.