A liquid crystal display device, comprising: a substrate; a plurality of light sources disposed on the substrate and configured to generate excitation light; a quantum dot film disposed in a light-emitting direction of the plurality of light sources; a plurality of reflecting plates disposed on the substrate and configured to reflect the excitation light emitted from the plurality of light sources; an optical layer between the plurality of light sources and the quantum dot film; and wherein: the plurality of reflecting plates and the plurality of light sources form a plurality of cavities arranged in an array, the plurality of light sources are located on bottoms of the plurality of cavities respectively, the optical layer is disposed between the plurality of cavities and the quantum dot film, and configured to partially transmit and partially reflect the excitation light, and the quantum dot film is configured to be excited by the excitation light to generate excited light; characterized in that, a ratio H/P of a height H between each of the plurality of light sources and the optical layer to a width P of each of the plurality of cavities is 0.1 ≤H/P≤0.25, wherein the width P of each of the cavities is a distance between two reflecting plates forming the cavity; a range of a transmittance m of the optical layer for the excitation light is 0.05≤m≤0.6; wherein each of the plurality of reflecting plates comprises a base plate parallel to the substrate and a side plate disposed vertically on the base plate, and the base plate and the side plate are both flat shape. a substrate; a plurality of light sources disposed on the substrate and configured to generate excitation light; a quantum dot film disposed in a light-emitting direction of the plurality of light sources; a plurality of reflecting plates disposed on the substrate and configured to reflect the excitation light emitted from the plurality of light sources; an optical layer between the plurality of light sources and the quantum dot film; and wherein: the plurality of reflecting plates and the plurality of light sources form a plurality of cavities arranged in an array, the plurality of light sources are located on bottoms of the plurality of cavities respectively, the optical layer is disposed between the plurality of cavities and the quantum dot film, and configured to partially transmit and partially reflect the excitation light, and the quantum dot film is configured to be excited by the excitation light to generate excited light; the plurality of reflecting plates and the plurality of light sources form a plurality of cavities arranged in an array, the plurality of light sources are located on bottoms of the plurality of cavities respectively, the optical layer is disposed between the plurality of cavities and the quantum dot film, and configured to partially transmit and partially reflect the excitation light, and the quantum dot film is configured to be excited by the excitation light to generate excited light; characterized in that, a ratio H/P of a height H between each of the plurality of light sources and the optical layer to a width P of each of the plurality of cavities is 0.1 ≤H/P≤0.25, wherein the width P of each of the cavities is a distance between two reflecting plates forming the cavity; a range of a transmittance m of the optical layer for the excitation light is 0.05≤m≤0.6; wherein each of the plurality of reflecting plates comprises a base plate parallel to the substrate and a side plate disposed vertically on the base plate, and the base plate and the side plate are both flat shape.