Pei Xi is a book of Chinese characters written by Guo Zhongshu. It epitomized the dictionaries of Chinese characters which are produced since WeiJin. Nowadays, it is worth standardizing Chinese characters and researching their developing rules. Pei Xi has three parts .The first part is the theory about Evolution of Chinese characters . This thesis will mainly analyze Guo Zhongshu’s theory about Chinese characters and their evolving rules , and discuss its significance in philology. This thesis will also provide some reliable reference materials for case study. The author will draw a conclusion by summing up the values of Pei Xi, as well as its influences.