The aim of this study was to investigate the color subarea judgment algorithm in multi-color separation based on spectrum. A color subarea judgment algorithm based on spectrum was proposed. The color subarea judgment algorithm was designed by introducing characteristic spectrum extracting and matching. On account of the parameters in the algorithm progress, the experiments were designed for calculation. The optimal subarea judgment results could be obtained under the following conditions: the value range of characteristic spectrum was divided into 12 levels, the differences between the target spectrum from subarea and target spectrum from the minimum distance of all subareas were smaller than 14% , while the RRMS and color difference between the predicted and target spectra were smaller than 0.01 and 1.5, separately. The exam indicated that the judge count of each patch was 1.93, which was about 24% volume of the circulation algorithm. The proposed color subarea judgment algorithm based on spectrum could exactly judge the target subarea where the color existed in an efficient manner, which simplified the multi-color separation progress based on spectrum.