A practical modeling for inhomogeneous coatings, which are prepared by double-source co-evaporation, is proposed in this paper, and then, the relationship between the deposition rate of inhomogeneous coatings and that of double-sources co-vaporation is discussed. The deposition rate of inhomogeneous coatings is close to the sum of the evaporation of the two materials when their bulks are close to or the amount of small molecules is far more than big ones. When the bulks of molecules of the two materials is different, the deposition rate of inhomogeneous coatings will vary with the ratio of their bulks and their deposition rates. Some deposition rates of inhomogeneous coatings in different situations are also detailed in this paper.