Abstract: The rhyme scheme of to-and-fro is a sort of tonal pattern that Zheng gu and other poets developed for modern "Cstyle poetry in the late Tang Dynasty. It is characterized by rhyming two words at different ends of verse that are neighboring but un-rhyming interchangeably. "dong", for instance, can not be rhymed with "dong", and "han" not rhymed with "shan". For they belong to different rhymes which can not be rhymed interchangeably. It is due to this rule that the rhyme scheme of to-and-fro appeared in the regulated verse in miscellanies style, which can not be used in a pent syllabic quatrain or a heptasyllabic quatrain. The first user of this rhyme scheme is Li He.