A luminance adjusting method for a display screen of an electronic device includes the following steps. Firstly, a current brightness value and a current imaging color value of the display screen are recorded. In response to the user's operation, the light output of the display screen is adjusted. Consequently, the adjusted brightness value is equal to a default brightness value and the adjusted imaging color value is equal to a default imaging color value. Meanwhile, the display screen is operated in the healthy display mode. In response to the user's additional operation, the light output of the display screen is adjusted. Consequently, the adjusted brightness value is equal to the recorded current brightness value and the adjusted imaging color value is equal to the recorded current imaging color value. Meanwhile, the display screen is restored to the normal display mode.