A display mode adjusting method and a display mode adjusting module executing the adjusting method are provided. The method includes the following steps: generating a saturation adjusting output color according to an input color to adjust the saturation; obtaining a relative color temperature adjusting parameter according to a target color temperature and an original optical characteristic of a display device; generating a color temperature adjusting output color according to the saturation adjusting output color and the relative color temperature adjusting parameter to adjust the color temperature; obtaining a brightness adjustment value according to the brightness of ambient light to adjust the brightness. Therefore, the display mode of the display device is adjusted to suitable for reading, which avoids the eyestrain when the users read for a long time.