In a railway track, the sleeper’s responses on a non-homogeneous foundation have been investigated by researchers focusing on the foundation behavior along the rails. However, the foundation can also vary along the sleeper length, particularly when the track is newly tamped. The foundation at the sleeper center is often weaker than those under the rails and this non-homogeneity directly affects the sleeper responses. This paper presents a new model to calculate the influence of such foundations on the dynamic responses of the railway sleepers. This model is developed by combining a finite element model for the sleepers and foundation and a model of periodically supported beams subjected to moving loads for the rails. In this paper, the foundation contains three parts with different mechanical behaviors. The sleeper’s responses can be calculated by transforming the finite-element dynamic stiffness matrix to the one considering the boundary conditions and the relation between the rail seat forces and rail displacements governed by the beam model. This method reduces all the degrees of freedom of the railway track to its one period which gives a substantial reduction in computational time. The numerical applications show that the more homogeneous (so-called consolidated) the foundation is, the larger the sleeper strain is at its center. This result shows the potential application of the sleeper responses to estimating the consolidation level of the foundation.