The concepts and models of visual gray balance were proposed and applied in gray component replacement of color separation process. Visual gray balance data was acquired by look-up-table based on chromaticity of visual gray. The equation between K and CMY was established based on neutral gray density. 4 kinds of replacement ratio were assigned replace the gray component of CMY color patches. The experiment results showed that when the replacement ratio is 0. 4, the color difference between the calculated and the original gray color patch is smallest; the color gamut is expanded in light and middle tone.