The structural change of polyacrylonitrile was investigated by iodine sorption in aqueous 1$_2$/KI solution. lodines could penetrate into the crystalline phase of polyacrylonitrile and disturb the laterally ordered polyacrylonitrile crystals below the low concentration of which I/M=O.33. Beyond this I/M up to 0.77, these iodine ions were found to form a linear lattice of about 3.1 A spacing like as in other systems and to orient parallel to the orientation axis in the crystalline phase of polyacrylonitrile. The 5.8A, 4.1A, and 3.9A diffraction intensities for polyacrylonitrile-iodine complex were observed on equator, which increase with increasing iodine concentration in the sorbed phase. These observed diffraction intensities and sorption-desorption behaviors suggest that the iodine which penetrates into crystalline phase intercalates between molecular rods of polyacrylonitrile without a conformational change, and forms a new ordered structure with the parent polymer.