It is very important for us to explore and forecast the change of U.S. dollar exchange rate. From the perspective of history and politics, this paper describes the evolution of the decision-making body of the U.S. exchange rate policy, and analyzes the position of the U.S. Congress and the Treasury Department in the process of making the U.S. exchange rate policy. Today's Treasury Department has great influence in the formulation of American international economic policies. However, Congress maintains the supervision of the treasury department according to the constitutional power, and its legislative power ultimately controls the formulation of the exchange rate policy of the United States.