Two-dimensional non-linear hydrodynamical equations are solved by using perturbation method and treating slopping beaches as bottom boundary conditions so that a kind of solution for nonlinear progressing waves is obtained. The first order of approximation is the same potential function as used by Biesel, and the second order is calculated numerically. Based on the solution, wave characteristics before breaking, especially the wave set-down, are discussed. It turns out that for the whole course of waves propagating from deep to shallow waters the theory proposed in this paper has a wider valid range of application than others. Two-dimensional non-linear hydrodynamical equations are solved by using perturbation method and treating slopping beaches as bottom boundary conditions so that one kind of solution for nonlinear progressing waves is obtained. The first order of approximation is the same potential function as used by Biesel, Based on the solution, wave characteristics before breaking, especially the wave set-down, are discussed. It turns out that for the whole course of waves propagating from deep to shallow waters the theory proposed in this paper. has a wider valid range of application than others.