The possible crystal structures of I-PP have been investigated by means of the theory of crystal symmetry.1.The dichromatic space groups of C2/c have been derived. Arrangements of the helical chains in these dichromatic space groups have been studied. Five possible space groups of I-PP (α-form) were given.2.A model of the crystalline structure of the a-form I-PP in which Cc and p2/c space groups are consolute has been proposed from the crystal domain theory.3.The arrangements of PP helical chains in a hexagonal crystals β-form have been inves-tigate. The most possible unit cell with nine chains passing through the cell has been suggest-ed. that is a R-type cell in which PP helical chains were placed in a semi-random fashion.