To address the problem of the influence of mineral pigment particle size on optical properties and color, this paper combines light scattering theory and Kubelka-Munk theory to construct an optical model of single pigment particles, map it to the optical properties of the pigment media group, and establish a differential mapping model of spectral reflectance, scattering coefficient and absorption coefficient. The experimental results show that the pigment particle size has a significant negative correlation with the scattering coefficient, spectral reflectance, luminosity and tri-stimulus values. This study verifies the rationality of combining optical theory and color theory, reveals the mechanism of particle size variation on the optical properties and chromaticity values of mineral pigments, and provides some theoretical tool value for the restoration of painted relics in computer color matching.