The Bai language, as a sister language of Chinese, has ever been an enigma of Sino-Tibetan family. To solve this enigma, the tree structure of Sino- Tibetan family as the background should be checked first. As the Bai language has a long-term contact with Chinese, the reconstruction of Proto-Bai becomes necessary in order to exclude late borrowings from Chinese. Studies along this way not only shed light on the formation of Proto-Bai, but also on the formation of Chinese. It has been noticed that lexical items may reflect the partial connection between languages. Looking into more basic functional items like negators in Bai dialects, it is suggested that some surrounding Yi languages may have played a role in the evolution of the Bai language. The multi-language ecology of the Bai language is similar to Chinese, especially at the stage of initial China.