Azurite, malachite green, and crystal were selected to get mixed with different ratios so as to measure the spectrum reflectance of the mixtures. The absorption coefficient K and scattering coefficient S value of three kinds of pigments were calculated individually based on double constant K-M theory. Then through computer color matching, the theoretical values of the color reflectance of mixed pigments were obtained owing to the additive property of the absorption coefficient and scattering coefficient. Compared with the former values of spectral reflectance from direct measurement, the color difference and RMS calculation could be worked out. At the same time, single K-M constant theory after pigment matching was conducted by means of computer color matching assisted by k/s values of the pure pigment so as to calculate the corresponding spectral reflectance values. By comparing the spectral reflectance of single color K-M theory and that from actual measurement, the color difference and RMS were calculated. At last, evaluation of the results of single and dual constant K-M theory of color matching was carried out, in which a relatively satisfactory result was obtained when dual constant K-M theory was used in the case of mixing three kinds of pigments.