A theoretical model calculating the surface total integrated scattering (TIS) of multilayer optical coatings is presented. The new model assumes that the rough interface and surface of the coatings are very thin zones with inhomogeneous micro constructure, which can be substituted by adequate number of homogeneous sub-layers, refractive indexes of which are constant and meet the exponential distribution. The formula of TIS is deduced by using the matrix method. For ZrO2 coatings deposited on K9 glasses by the electronic beam evaporation method, the TIS result calculated by the new model is in better conformity with the measured value by the scatterometer than that by the uncorrelated surface roughness model.