A backlight structure is provided. The backlight structure includes a substrate, a light emitting diode array layer disposed on the substrate, a planarization layer disposed on the light emitting diode array layer, a composite medium layer disposed on the planarization layer, a metal gate line layer including a plurality of metal lines disposed on the composite medium layer, a fluorescent layer disposed on the metal gate line layer, and a diffusion layer disposed on the fluorescent layer, wherein the composite medium layer includes a first medium, a second medium, and a third medium, the second medium is interposed between the first medium and the third medium, and each of a refractive index of the first medium and a refractive index of the third medium is less than a refractive index of the second medium.