We stutied the nonlinear modulation of the gravitation surface-tension waves on the interface between two layers of imcompressible inviscid fluids which are contained in a rectangular waveguide with horizontal solid walls, by the meth rd of multiple scales technique, and generalized the theory of Larraza and Putterman. Including the surface-tension effects, we found that the first order modulated wave satisfies the cubic Schrodinger equation. Then me derived the non-propagating solitary solution, and made some discussion on the results obtained.