In this paper, a transformation is given, which transformed the dam seepage free-boundary problem into a fixed-boundary problem of a quasi-Liner elliptic equations on a rectangular (as 2-dimension) or cubic (as 3-dimension) doma in. The latter problem is solved easily to use the finite-difference method and the SOR arithmetic. The method is given in this paper, is suitable for 2-dimension or 3-dimension and at that time there are a well.