The invention provides a brightness enhancement film, a preparation method therefor, and an optical
composite film. The brightness enhancement film sequentially comprises a base material, a condensation layer and a
refraction layer from the bottom to the top, wherein the condensation layer consists of a plurality of condensation structures. The condensation structures are respectively provided with a bottom surface which contacts with the upper surface of the base material. The
refractive index of the
refraction layer is greater than the
refractive index of the condensation layer, and the upper surface of the
refraction layer is provided with a concave-
convex structure which is matched with a concave-
convex structure on the upper surface of the condensation layer. In the above brightness enhancement film, the upper surface of the condensation layer is provided with a refraction layer with relatively high
refractive index in an attaching manner. The upper surface of the refraction layer is enabled to be provided with the concave-
convex structure matched with the concave-convex structure on the upper surface of the condensation layer, thereby equivalently enabling the surface of the brightness enhancement film to maintaining the geometrical shapes of the condensation structures. The refraction layer with the high refractive index can remarkably improve the condensation degree of light on the brightness enhancement film, thereby improving the brightness
gain of the brightness enhancement film. Meanwhile, the geometrical shapes of the condensation structures are maintained, thereby preventing the arrangement of the refraction layer from causing the change of the geometrical optical effect.