Based on historical and realistic materials, this paper explains that the change of foreign policy of sovereign countries leads to the change of international relations because of the change of national interests. There is a wise saying in national diplomacy that "there are only eternal interests, but no eternal friends". The change of national interests is the fundamental reason that affects foreign policy. For example, after the end of World War II, the relationship between China and Japan deteriorated to the verge of breaking diplomatic relations. Until the 197s, the influence of the Cold War expanded, China became hostile to the Soviet Union and normalized diplomatic relations with the United States. China and Japan fought against the influence of the Cold War and the threat of hegemonism, and the two countries put aside their differences and re-established diplomatic relations. Interest comes first in national communication.