The Han dynasty was the birth-period of calligraphy, the sprouting times of calligraphy theory, and the quickening period to investigate Chinese characters. This was not a coincidence. Calligraphy theory came from the cause that people looked at calligraphy as an art. As a result, it has influenced the field of researching characters, explaining theories about characters themselves, and cultural concerns about the transformations of characters since that period. This paper, as a basic work of researching letters, has summarily studied the books, the expansion steps, and the researching origin about the theories of letters before 『ShuoWenJieZi(設文解字)』. These studies, being grounded on the viewpoint of calligraphy history, will be the key point in investigations about the connections between the writing theory and the writing skill that were born at the same time with the theories of letters in the Han dynasty. The main points of this paper can be summarized in the following ways: 1. The central point of the theories about the letters before 『ShuoWenJieZi(說文解字)』written by XuShen(許愼)is 『The book: CangJieBian(倉趙編)』. 2. The theories about the letters in the Han dynasty are closely connected with the historical events of the Qin(泰) dynasty. 3. The studies of characters in the Han dynasty had been developed by the scholars who dreamed of the revival of classical literature. 4. The studies of characters in the Han dynasty had been developed in company with the studies of ancients books. 5. 『ShuoWenJieZi(說文解字)』written by XuShen(許愼) means the colligation of the LiuShu theories(六書設) existed in the Zhou(周) dynasty, and it can be said to be the cornerstone of the theoretical development of Chinese characters.