A luminance sensing system and method and a computer program product thereof are provided. The system includes: a first luminance sensing unit, arranged at a first position, and used for sensing a light ray luminance at the first position to generate a first illumination value; a second luminance sensing unit, arranged at a second position, having a displacement unit, and used for sensing a light ray luminance at the second position to generate a second illumination value; and a computing unit, electrically connected to the first luminance sensing unit, the displacement unit, and the second luminance sensing unit, and used for acquiring the first illumination value and the second illumination value, acquiring luminance range information by using the first illumination value. When the second illumination value does not conform to the luminance range information, the computing unit controls the displacement unit to move the second luminance sensing unit.