A backlight adjustment method and a backlight adjustment system are provided. The backlight adjustment method includes a compensation phase. The compensation phase includes: controlling a light source to respectively emit light having a plurality of first illuminations; detecting a plurality of backlight parameters of a display device under the light having the plurality of first illuminations, and calculating a brightness compensation coefficient of the display device according to the plurality of backlight parameters; and adjusting a backlight coefficient of the display device according to the brightness compensation coefficient, so as to compensate for backlight brightness of the display device.