In ancient times, internal security refers to the institutions and personnel used to maintain the internal security and stability of the country. In ancient China, internal security played a very important role. Its members are mainly selected by the emperor himself and are responsible for the safety and sacrificial ceremonies of the emperor and the royal family. Members of internal security need to undergo strict selection, training and examination to ensure that they have sufficient loyalty and skills.

The duties of internal security include guarding the palace, guarding the emperor, guarding the palace and the royal mausoleum. They are also responsible for evaluating officials at all levels, guarding court catering and supervising maids-in-waiting, which are closely related to the power of officials. Therefore, internal security sometimes became an important means for the emperor to exercise and consolidate his power.

In addition to ancient China, many other countries also had internal security. For example, in Japan, it is called the "Kingsguard" and is responsible for protecting the safety of the emperor and members of the royal family. In the Middle Ages in Europe, internal security was the personal guard of the apostles and the royal family, such as the "Royal Guard Brigade" in France and the "Royal Guard" in Britain. In a word, internal security has played an important role in maintaining the power of rulers and expanding their ruling power in history.