It has been more than 40 years since Yunmeng Qin bamboo slips were unearthed. As the first batch of Qin bamboo slips unearthed, it is close to the truth of the Qing dynasty. Because the unearthed bamboo slips are clear and easily to recognize, most of them are complete, which provides favorable conditions for the in-depth study of Yunmeng Qin bamboo slips. To start with, the aim of this paper is to explore the special words used in the development period of modal particles, to clarify the development context of the evolution of modal particles, and to sort out the internal differences of the evolution of modal particles in Yunmeng Qin bamboo slips. We give a possibility for Yi (殹) and Ye (也), which seems to alternate between Yunmeng Qin bamboo slips. Secondly, we found the factors to these change: dialect, country, written forms and customs. Also, we set many examples to prove Yi (殹) and Ye (也) in Yunmeng Qin bamboo slips truly alternative. The time of Yunmeng Qin bamboo slips was written at about the end of the Warring States period to the early Qin Dynasty, which was the time when the words were not solidified. In this period, the use of words was chaotic, and modal particles showed different use of words because of their distinctive regional characteristics, that is, the diversification of writing forms. Especially, Yi (殹) and Ye (也) were two modal particles in Yunmeng Qin bamboo slips. As a Qin character, commonly seen in Yunmeng Qin bamboo slips, Yi (殹) is often used as a modal particle in the slips of Qing dynasty, which has been discussed by senior scholars such as Li Xueqin and Chen Zhaorong. Mr. Li talked about Yi (殹) and “habitually seen in Qin Bamboo Slips” in his article “an Investigation of Ancient Philology of Qin Bamboo Slips”; When discussing the evolution of Qin characters, Mr Chen interpreted Yi (殹) as a mood auxiliary word with both regional and contemporary characteristics.

The article states that the writing style determines the forms ofChinese Characters during the process in shaping the characters by analyzing the Characters both in Pre-Qin Days and in Qin Dynasty. In other words, the way of writing influences the result of writing------ the forms of Chinese character directly, moreover, any kind of change in characters’ evolution stems from the slight difference from the previous writing style. Characters are presented by using writing, characters on Bamboo or Wood strips in Qin Dynasty are kept more in the inking words in the early forms of Chinese characters; meanwhile , writing style in Qin Dynasty is a transitional form in the change from seal script to clerical script; at the same time, it includes both the writing motivation of seal script and other writing styles, such as, clerical script, running script and cursive script in the following periods and conceives rich connotation in writing styles. So, we know that , to some extent, the writing style can restrict or improve the process of characters’ evolution by researching the writing styles’ influence on the following characters’ shape. And as an internal factor, it is writing style itself that influences the Chinese character’s shapes. In this way, we push the traditional static research of forms of joining different parts to form the Chinese characters and that of changing rules of different parts in Chinese characters to the dynamic level in Chinese characters’ research.