A method for adjusting saturation degree and a color adjusting system are provided. The method for adjusting saturation degree includes the following steps. A hue circle is divided into a plurality of hue regions, and each of the hue regions is divided into a plurality of saturation regions according to at least one saturation threshold. A plurality of first input saturation degrees of a first saturation region of a first hue region of the hue regions are weighted by a first weighting formula for obtaining a plurality of first output saturation degrees. A plurality of second input saturation degrees of a second saturation region of the first hue region of the hue regions are weighted by a second weighting formula for obtaining a plurality of second output saturation degrees. The first weighting formula is different from the second weighting formula.