The work aims to research the variation trend of CMYK four-color ink transfer rate under various printing pressures. The control variable method was adopted to deeply study the relation between the offset printing pressure and the ink transfer. The offset printing paper of printability tester IGT C1-5 was used. The experiment was conducted at the same printing speed and at different printing pressures. The ink transfer rate data of the four CMYK inks on the offset printing paper under various printing pressures were obtained. By using software Matlab to simulate the data obtained, the curve of relationship between the printing pressure and ink transfer rate and the equations were obtained. In conclusion, the ink transfer rate remarkably increases with the increase in the printing pressure. When printing pressure on the offset printing paper reaches about 450 N, the ink transfer rate is the largest, and then the ink transfer rate decreases with the increase in printing pressure. Upon the analysis by the software, the printing ink transfer rate and printing pressure are in the relation of quintic curve.