(1) Change: The Tang Dynasty improved the system of three provinces and six departments, and the governors of the three provinces were all prime ministers, and the one-phase system became a multi-phase system.

Function: the three provinces cooperate and contain each other to improve administrative efficiency; It not only avoids the autocratic power of ministers, but also strengthens them.

Imperial power.

(2) The conflict between imperial power and legal power. Imperial power is restricted by phase power and legal power.