The research aims to explore the Chinese character “jì (既)” in pre-Qin period. The research focuses on the font change of jì (既) in pre-Qin period. Throughout the discussion, the understanding of jì (既), including of different fonts, such as , , can be known. We can know that the pronunciation of jì (既) has a close relationship with qì (氣), according to the use of related characters, for example, ài (㤅), jì (䊠), xì (餼) and so on. Talking about the meaning, there are seven meanings of jì (既), such as finish eating, end, whole, already, since, jì ér (既而, soon afterwards), jì yǐ (既以, farther), xì (餼, foodstuff). The results will be beneficial to facilitate understanding of academic writing materials and expand Warring States research in other aspects.