A method for adjusting saturation by distinguishing a plurality of color systems and color system zones corresponding to the color systems from a C.sub.b-C.sub.r coordinate, and finding the corresponding color system zone including the to-be-adjusted pixel of a digital color image. Thus, the first chroma C.sub.b and the second chroma C.sub.r of the to-be-adjusted pixel may be adjusted after the corresponding color system zone is found. This method can adjust a chroma of a specific color system without influencing the chroma of other color systems.