Under the situation of declining economic growth and strengthened external challenges，the United States is unable to operate its high-cost hegemonies． In recent years，the U．S． still focuses on its own interests，advocates “U．S． priority”，implements exit strategy and strengthens containment on China and launches trade war，which reflects the recession of its hegemony． Influenced by the strategic misjudgment resulting from Thucydides Trap and the nature of imperialist expansion，the United States will strive to maintain the long-term existence of hegemony． In the post-hegemonic era，China will actively promote the construction of a new international order and seize the important historical opportunity of peacefully rising in meeting challenges．