The paper was aimed to build a model used in color matching of spot color ink. Based on K-M theory and weight factor method of spectrophotometric color matching, a model of color matching for offset printing ink was established. Through calculating the color difference between the sample and matching color, the model precision was tested. The color difference of matching color was less than 6, meeting the requirement of color reproduction. The model established using the presented method had a relatively high precision and could be used for color matching.