In the early Tang Dynasty, senior officials in the Middle Shu, subordinates in the middle shu, and senior officials in the Middle Shu discussed state affairs together, all of whom were prime ministers. The prime minister is an official who assists the emperor in managing the state affairs.

"New Book of Tang · Baiguan Zhi" : "Zuo Tianzi chief baiguan, governing everything, its heavy duty".

Later, because before Emperor Taizong ascended to the throne, although he had served as a minister, his subjects avoided and dared not take up their posts, so they took "poshi" as the senior officials of the minister, and his subordinates, Zhong Shuling, as prime minister.

"Book house yuan turtle · prime minister general preface" records, since the Sui Dynasty, there are "or to his official participation in the handheld game and exclusively in charge of the government, and for the assistant". In tang Dynasty, because of the chancellor's taste and respect, people refused to grant people easily, so they often assumed the position of prime minister by his official, and under the guise of his official title. For example, during the reign of Emperor Taizong of the Tang Dynasty, Du Yan took part in the administration of the Ministry of Civil Affairs, wei Zheng took part in the administration of state affairs as secretary, and later, they were called "taking part in the discussion of gains and losses", or "taking part in the administration", etc., with different names, but in fact they were all prime ministers.