Methods and an apparatus for setting brightness of a display screen of an electronic device based on ambient light brightness. The method includes acquiring by a light sensor on the electronic device a measured brightness of ambient light having an actual ambient brightness at where the electronic device is located; detecting whether the light sensor faces away from a light source in the environment; when it is detected that the light sensor does not face away from the light source, determining a reference backlight brightness level according to a backlight brightness level-setting function comprising a correspondence between actual ambient brightness levels and backlight brightness levels, by using the measured brightness as actual ambient brightness; and setting an actual backlight brightness of the backlighted display screen to the reference backlight brightness level; and when it is detected that the light sensor faces away from the light source, setting the actual backlight brightness of the backlighted display screen at a level different from the reference backlight brightness level.