Abstract: Based on the basic goal of ensuring the balance between national military security and the stability of democratic system, under the leadership of the Federalists, the U.S. Constitution established the system of civilian control over military forces. As the basic structure of civil-military relation in the United States constitutional system, there is a multi-dimensional decentralization between the legislative power and executive power, federal and state, standing army and militia. With the development of military and politics, the static constitutional rules structure was changed by a dynamic game. The Standing Army has been strengthened, while the militia has transformed from a traditional military force that embodies the spirit of republic into another form of standing army in essence, thus reshaping the substantive meaning of the militia clause in the Constitution. In the course of the game between the administrative power and the legislative power, the administrative power has been expanded to be a stronger and more complete power to command the military forces, which has also reshaped the decentralization clause of the Constitution. In contemporary society, the development of military professionalism leads to the homogenization of civil servants and military elites, who are better at dealing with political problems. At the same time, the conflict of civilizations in a pluralistic society strengthens the political significance of military action and promotes the conservatism of social ideology. These two factors have further led to strengthened the political character of military force and changed the traditional civil-military relation. It is the reasons why the Trump administration has shown a new tendency in the civil-military relation that the influence of military forces on politics has been more prominent.