The admixture of Spot-color ink is generally determined by experience to make sure the type of primary color and the use of each ink, and then change the proportion of each primary color by the chromaticity control or visual experience. While this approach is difficult to admixture a qualified spot color ink, it also easily leads to the waste of ink. This paper did many researches and experiments on how to establish a spot color matching system based on the calculation of ink. Through the calculation of the largest ink thickness on paper, the model of the total estimated amount of printing based on image is established. Then this paper adopts the method of three stimulate value matching to establish the spot-color matching model based on Kubelka-Munk law. Through the combination of these two models above, spot color matching system based on ink calculation is finally established, and verified through the actual printing.