Abstract Conflicts between idealism and realism, isolationism and internationalism run through US foreign policy. After the Cold War, three theoretic trends of thought that influence current and future US Diplomacy have emerged. The first one is Neoisolationism whose theory is: to set up foreign policy and targets on the basis of national interests; to put domestic issues as the center policy; to establish international intervention mechanism; to reduce US obligations abroad. The second is Neointervenism which advocates: civil war does not belong to domestic affairs, human rights is above sovereignty; to establish international intervention mechanism; to replace the old "containment strategy" with "expansionism strategy"; to advocate preventive diplomacy. The last is Pragmatic Internationalism whose theory is: the U.S. must pursue active participation policy since the international situation becomes uncertain after the Cold War; carry out cautious foreign policy because it is the most, but not the only, powerful country in the world, it is only the most powerful among many powerful nations; revitalize traditional moral and cultural values in order to make US hegemony possess political and philosophical legitimacy; China issue has attracted wide attention from pragmatic internationalists. In interacting upon one another, these three trends of thought produce influence in US diplomacy in different degrees according to specific condition. The Pragmatic Internationalism will become the theoretic mainstream on which the US policy makers depend.