The existence of structural order is found in the polyacrylonitrile (PAN)-iodine complex obtained by immersing PAN film in an aqueous solution of I2/KI. We provide an interpretation for the key features of this structural order and for the structural change of PAN by iodine sorbing. The observed diffractions suggest that iodine penetrates into the crystalline phase of PAN at relatively low iodine concentrations and are intercalated between PAN molecular cylinders in the form of polyiodine columns that are composed mainly of I5(-) (most likely the I2/I3(-) complex). Pseudohexagonal crystals of PAN are expanded uniaxially by replacement of PAN molecular cylinders by the polyiodine columns. The intercalated polyiodine column layers are arrayed parallel with PAN chain layers in the crystalline phase. The results led to a proposal of an intercalation model for the crystalline structure of the PAN-iodine complex. The crystalline structures are expected to exist with two different types of the polyiodine layers. The crystalline transition between these structures occurs by thermal mobility of PAN chains.