A simulating model of emissivity of infrared stealth coating based on Kubelka-Munk theory is put forward. Taking aluminum particles as pigments, using Maxwell-Garnett effective medium theory, the relationship between equivalent refractive index of coating and wavelength is calculated and analyzed. Based on the mutual interaction of the electromagnetic wave and pigments, adopting geometrical optical theory, scattering and absorption coefficients of the coating are calculated. Effects of aluminum particles′ parameters, such as size and volume, to the emissivity of coating are analyzed quantitatively. The result shows that the proposed model could be used to guide the preparation of infrared stealth coating.