A light guide plate in a backlight module includes a light guide layer, a carrier layer, and a reflection sheet. The light guide layer includes a first surface and an opposite second surface. A plurality of light guide outlets is formed on the first surface. The carrier layer includes a third surface and an opposite fourth surface. The third surface is adhered with the second surface. The carrier layer defines a receiving groove having a fifth surface parallel with the third surface. A plurality of through holes passes through the fifth surface to the third surface to expose portions of the second surface. The reflection sheet is arranged on the first surface and is aligned with the receiving groove.