The national interest is the essential that drives interaction among countries in the international community. As the manifestation of the basic national needs, the national interest decides not only the orientation of national policies but also the national strategic goal-setting; we can even think it is the supreme principle for national diplomatic policy-making and implementation. After the end of Cold War, profound changes have taken place in the international community with speeding up the economic globalization and the world multi-polarization. From the view of the international political structure, the power among the international community is tending to a balance, and the interdependence between countries is strengthening significantly. While facing more and more common interests, it means the autonomy to achieve the national interest continues to decline, and how to realize the national interest is becoming complex. Considering that countries have adjusted their diplomatic policies, the willingness of win-win cooperation is tending to ascend in the international community. A country should not only consider the national interest in a special period but also the long-term national interest; not only consider its own interest but also the common interest of mankind. The national policy-making and adoption should not consider from the viewpoint of itself, because the policy-making and adoption are constrained by other countries’ interest. This paper will use the constructivism theory to analyze the 2 development of China-EU relations. National identity is built in the process of interaction. In this process, the identity can be cognized by other actors; the cognition is affected by the external environment including international system, international co-operation culture as well as the internal qualities such as national powers, ideologies and values. The cognition finally constructs the corresponding identity of the actor, which can also define interests and desires, thus affects the development of bilateral relations. In a different stage, EU’s perception of China’s national identity is different; procedure is composed of four stages which are an immature partner, a friendly partner, a strong challenger, a powerful and responsible country. At the same time, each stage has a corresponding national identity, namely a primary participant of the international community, an open socialist country, a challenger of the international system and a responsible country. Here, the main viewpoint is that the different stage defines different national interests and leads to different policies and actions toward China, thus also affects the development of China-EU relations. The positive cognition will lead to the co-operation between China and EU, while the negative cognition will cause the breaking-up of bilateral relations.