Abstract: In the present article, the properties of polaritons in a disordered material are studied under the Coherent Potential Approximation. Our main results are ag follows:(1) The concept of an effective wave vector can be used to describe the polariton of a dielectric glass, and the criterion for the existence of effective wave vector is also given. (2) The polariton dispersion of a disordered material is similar to its crystalline counterpart, which is consistent with recent experiments. (3) In the sense of the attenuation due to the disorder of the structure, the phonon-polariton is bettor than the exoiton-polariton in long-distance optical fibre communications. As an application of the present theory, we have derived the dispersion of guided-wave polaritons in a planar disordered waveguide.