The research aimed to solve the problem that the predefined black printing plate cannot adaptively determinate the black generation curve based on the characteristics of the original ink coverage. The distribution of neutral gray blocks was investigated using the microscopic analytical method to comparatively analyze the chromatic aberration before and after substitution of saturated colors. The starting point of the black printing plate was associated with the screen lines and the dot shape. The determination of the starting point of the black printing plate should be based on the principle of protecting the tonal level of light colors in images. In the experiment, the square dot printing with traditional 150 Lpi screen angle was adopted and the starting point of the black printing plate was determined to be 13% dot area coverage. And the black amplitude should be determined on the basis of optimal rendition of saturated colors and the principle of largest black substitution with reference of Δ E76 less than 3 for saturated aberration. In GCR process, the principle of largest black substitution with reference of ΔE76 less than 3 for saturated aberration can retain the saturated chroma, meanwhile, save the usage of color ink to the largest degree, and the determined black substitution curve can be used to guide the establishment of the device link profiles to ensure more accurate image color conversion.