By using HR, HC, SC and NPDC parameters in G7 technology to control the gray balance of the printing machine, the experimental scheme of the objective and subjective evaluation was adopted. By measuring the printing proofs before correction and corrected by G7, with the objective measurement data and the subjective test sample, the comprehensive printing quality was obtained by using the qualitative evaluation methods and quality indicator equation in order to assess the effectiveness of control. Results showed the printing’s HC_CMY value after the gray balance controlled printing machine had a 8% deviation compared with the standard of G7, and 24% higher than that before correction; HR_CMY value had a 3.7% deviation compared with the standard of G7, and 10.3% higher than before correction, there was no deviation in HC_K, HR_K value and the standard of G7; the NPDC of CMY had a better fitting degree with the standard curve of G7 in the range of 0 to 40%; in 40% to 50% and 55% to 70% of the standard deviation of the curve was in the range [0, 0.05]. The neutral gray index score in image quality was 18.3% higher than that before the gray balance control. The practice and evaluation methods indicated that the gray balance control could effectively control the print quality.