The digital proofing technology to accurately simulate the custom spot color and screen printing of spot color was studied. On the basis of accurate spot color simulation, by analyzing the variation trend of density difference between the proof sample and the printed sample along with dot value, the curve of density difference corresponding to dot data was fitted by staged fitting algorithm. After adjustment of the actual density, the accurate simulation of screen printing of spot color was carried out. Through this method, the customized spot color matching for digital proofing could be realized, and it could be applied to the fields containing a lot of spot color printing such as packaging printing, label printing and multi-media printing.