The present invention discloses a method of forming an optical sheet. The optical sheet comprises a substrate and a film. The substrate has a first surface and a second surface opposite to the first surface. The film has a third surface and a fourth surface opposite to the third surface. The third surface of the film is on the first surface of the substrate. The fourth surface of the film comprises a structure corresponding to a combination of a plurality of first convex shapes and a plurality of second convex or concave shapes superimposed on the plurality of first convex shapes.