Influence of different inhomogeneities on the spectral characteristics of dielectric single layers was discussed.Comparing with homogeneous coatings,it is found:the maximum of the film with positive change decreased, and with negative change increased ; the minimum of the film changed little when the inhomogeneity was small comparing with homogeneity film. Through the comparison of the film in theoretic and experimental,there are transitional layers between substrate and coatings, and the refractive index lies between them.