A model for the structure of filled polymeric composites has been developed. To simulate filler-filler and filler-matrix interaction on a meso level, the Voronoi polyhedron representation of smallest structural elements (filler particles) is used while fractal concepts are applied for the description of more coarse-grained structures. An iterative method based on the ideas of renormalization group transformations is presented to calculate viscoelastic properties such as the storage and loss modulus of the composite. The influence of frequency as well as the properties of filler and matrix on the effective viscoelastic properties of polystyrene melt filled with glass spheres has been elucidated in a wide concentration range. The calculations and the experiments are in good agreement. Moreover, model calculations coincide with results of percolation theory.