Abstract: Color measurement and control system can improve the product quality and efficiency of multi-color offset printing,and the technology of color to ink conversion is one of the key technologies of the color measurement and control system. First,the principle of the automatic color measurement and control system is given,then,the relationship between the quality parameter,such as the density,and ink amount is analyzed,and the conversion matrix between chroma and density is given. On the basis,color to ink conversion algorithm based on density and color to ink conversion algorithm based on chroma are designed,and the relevant algorithm flow diagrams are given. The algorithms are applied to the color measurement and control system. When there is density deviation or chroma deviation,the algorithms can calculate the adjustment of the ink key automatically to change the ink amount,then improve the color quality of the print.