Abstract: Based on Goodman model, which is used for simulating the touching condition between beams, a diffirential equation group of composite beams on Winkler foundation and its theoretical solution have been induced. The shear, tension and compression deformation in beam section due to the horizontal and vertical force in interlayer are considered through introducing a ``generalized interlayer reaction modulus''. This method raises the calculation accuracy, especially in the case of broken bi layer beams.