In the 21st century, great changes have taken place in the world and China. The rise of China makes itself the focusing point of the world. Is China a threat or an opportunity for the world? Many scholars and government staff are eager for answers. They want to know what Beijing’s grand strategies in the following decades. Under this condition, many journalists and outside observers notice one phrase: core interests. Since the first use by Chinese officials in 2003, the phrase core interest becomes common in Chinese diplomacy and foreign policies. It has been one of the most indicators to look into Beijing’s foreign relations. This thesis tries to find out Beijing’s exact definitions of core interests at different periods. To trance the evolution of this definition, I set up a database covering all the articles in People’s Daily which contain this phrase core interest. Based on the empirical analysis of the data set, I think, Beijing claims its core interests as an response to external violation or threat. According to my research, to maintain the national sovereignty and terroritial integrity is the primary purpose of China’s core interest diplomacy. Its definition is terrority-centric and flexiable, but become to be broad and abstract. After assessing the contemporary conditions and China’s past definitions, I believe that the South China Sea will almost surly be China’s core interests. And this may result a great challenge to Chinese foreign policies, the security and stability of Asia. I thins, contemporarily, China’s in transition and it’s foreign strategies are also facing a new turning point after Deng came into power. China’s core interests are most important indicators which deserve our full attention and long-term research