In the pre - Qin literature, the characters "ti", "pi", "nian" refer to "tear", "beast skin" and "year" respectively and it became "nasal discharge", "man's skin" and "age" respectively in the Han dynasty, which never appeared in the pre - Qin period. By studying the semantic changes in books of different times, the meanings of the above 3 characters, that frequently occurred in Neijing, are identical with those books of the Han dynasty. Hence, it can be concluded that Neijing can only be completed not early than the Han dynasty.