In ancient China, the secrecy of official documents can be traced back to the Xia Dynasty. According to historical records, Tai Shiling has "maps" (that is, important national records and archives of the country) "official collection"; during the Shang Dynasty, the history of keeping Tibetans was established An official position, responsible for keeping official government documents and books; the Zhou Dynasty inherited the tradition of the Shang Dynasty and collected the original documents in Tianfu, the earliest central archives institution in China's history. When the Qin Dynasty, the seal was sealed on the documents and passed on. The use of "sealing mud" in the process has become a common practice. In the Eastern Han Dynasty, the "sealing mud" used for the confidentiality of office documents turned out to be a metaphor for keeping guards. "Hou Han · Xiao Zhuan" records: "(王) Yuan please use Yimaru mud as the king to seal the Hangu Pass, and this will happen for a while. "It means that guards should be carefully sealed, and there should be no omissions. This text mainly introduces:. ['Secrets of Official Documents.', 'The evolution of the word "seal".', 'Evolution of archival storage methods.', 'Records of preservation methods in history books.']