A BLU includes a plastic frame, a heat-dissipating plate, an LED light bar, a light guide, and an optical film. The plastic frame includes a first horizontal part and a first vertical part connected with the first horizontal part. The heat-dissipating plate includes a second horizontal part and a second vertical part. A first through hole penetrating the first horizontal part and the first vertical part is set on the plastic frame. A hook is set on the end of the second vertical part. The second vertical part is close to the first vertical part and the hook clasps the first horizontal part.