The key parameters in printing control method based on G7 process were analyzed, which were HR and NPDC curves. In conditions of devices performance stable and standard materials, a printing test was carried out in terms of G7 process, and then the data were measured to draw NPDC curve. Gray balance calibration was carried out. At the last, the accuracy of the compensation values was tested and verified. NPDC curve was plotted again. It was founded that the trend of the NPDC curve is in accordance with standard curve.