NOVELTY - Preparing antireflection structure, comprises: (a) coating a layer of organic solvent solution of block copolymer having first polymer blocks and second polymer blocks on substrate modified with organic material; (b) solvent annealing resultant coating layer by placing coated substrate in atmosphere containing vapor of non-preferential solvent; (c) selectively degrading first polymer blocks; (d) filling inorganic filler into gyroid nanochannels; and (e) removing second polymer block matrix of layer by using an UV light exposure, calcination, organic solvent, and/or a supercritical fluid.    USE - The process is useful for preparing an antireflection structure (claimed) which is used in devices including flat panel displays, solar cells, omnidirectional reflectors, LEDs, LCD back-light modules, and windows.    ADVANTAGE - The process provides antireflection structure having low refractive index.    DETAILED DESCRIPTION - Preparing an antireflection structure, comprises: (a) coating a layer of an organic solvent solution of a block copolymer having first polymer blocks and second polymer blocks on a substrate modified with an organic material; (b) solvent annealing the resultant coating layer from step (a) by placing the coated substrate from step (a) in an atmosphere containing a vapor of non-preferential solvent so as to form a film of the block copolymer having the second polymer blocks as its matrix and the first polymer blocks having a gyroid nanostructure in the matrix; (c) selectively degrading the first polymer blocks to form correspondingly gyroid nanochannels in the matrix of the film; (d) filling an inorganic filler into the gyroid nanochannels in the matrix of the film in a liquid mixture of a filler precursor under so-gel conditions; and (e) removing the second polymer block matrix of the layer by using an UV light exposure, calcination, organic solvent, and/or a supercritical fluid to obtain a layer of porous inorganic gyroid network on the substrate. The first polymer is poly(L-lactide), poly(D-lactide), poly(lactide), or poly(caprolactone), and the second polymer is poly(styrene), poly(vinylpyridine), or poly(acrylonitrile).