Abstract: Chinese three-syllable-word has kept steady increasing from the pre-Qin period to modern times.It can be speculated that the number of three-syllable-words will go over two-syllable-words after hundreds of years.The trends of Chinese word-length are: monosyllabic word→double-syllabic word→three-syllable-word.And three-syllable-words as the main body of Chinese words will come into being, and the reasons are the following: their quick developing, their percentage increasing, their large number of nouns and modifying compound words and their developing law, which present their superiority.Moreover, basic unit of the language must fit in with complicated and rarefied of people's cognition, for the more minor the impact of social development is, the more lacking the significance of simplified voice.