An input device with a backlight function and a backlight color adjustment method are provided. The input device with the backlight function includes a casing, plural color light-emitting elements, a control module and a charge-coupled device. The control module provides electric power to at least two selected color light-emitting elements through a power supply circuit. By the control module, the chromaticity value of a mixed white light beam from the color light-emitting element is adjusted to be consistent with the chromaticity value of a white light beam, and the luminance value of the mixed white light beam from the color light-emitting element is adjusted to be consistent with the luminance value of the white light beam.