The issue of South China Sea is one of the hottest international disputes in South East Asia due its location amid the connection between Southeast Asia to Northeast Asia and the rich resources. The undecided maritime delimitation makes the situation more complicated. Because each one of the ASEAN Claims has her own consideration of the interest, their claims and policies confront from each other's, and no consensus has been reached. However, encountering the fact that China proclaimed the entire region of South China Sea, ASEAN Claims attempt to unit themselves to deal with the threat, to negotiate the issue of South China Sea with China as a whole, and attempt to internationalize the issue. Thus, this paper is aimed to realize under what circumstance, ASEAN Claims will tend to unite in the issue of South China Sea, or vise versa, in what circumstance makes ASEAN Claims tend to collapse. According to the "Balance of Threat," China's threat to South China Sea affairs leads the changing of the unity of ASEAN Claims directly, and influences the consistency of South China Sea's policy. Besides the United States, the other side of the balance of the two counter powers, the treat brought by China in South China Sea affairs is the key to influence the South China Sea policy consistency of ASEAN Claims. "South China Sea Core interest" is one of match instance.

南海爭端近幾年區域緊張情勢不斷升高。中國已將南海列為「核心利益」，而美國則將南海視為「國家利益」。基此，這顯現中美兩國在南海議題的積極作為，雙方在其處理南海議題的戰略架構下，兩國主要舉措均在外交與軍事層面上針鋒相對。外交上中國以「睦鄰外交」，穩定周邊局勢，美國則運用「前沿部署外交」拉攏東亞各國；兩國對於東協國家的態度將更為重視，亦是雙方外交戰略的重點所在，渠等均希望藉由東協國家的支持在南海議題上更有話語權。而軍事上中國以「反介入/區域拒止」的軍事作為防止域外國家介入其主權議題，而美國研擬「空海一體戰」除運用其強大的軍事科技實力外，欲結合各盟邦的力量，與其一同牽制中國的軍事行動。 綜上，在中美兩國相互的競逐作為下，佐以米爾斯海默之攻勢現實主義觀點，檢視中美兩國在南海之未來互動關係。潛在霸權國中國擁有眾多的人口與快速成長的經濟，並在南海整軍經武，試圖強化與東協甚或是東亞諸國的經貿互賴程度，且於處理亞洲事務中將美國排除在外，以取代美國擔任亞洲關鍵角色，尤其在南海的不妥協性，顯現出中國在此區域的主導性。另外，既存霸權國美國面對中國綜合國力崛起，則扮演「離岸平衡者」，融合「推諉卸責」、「均勢」之概念，拉攏東協及日本、印度等相關國家，共同制衡南海區域的權力失衡狀態，鞏固霸權地位。中美雙方皆將南海問題的層級提高，並且均欲爭取南海區域之領導地位，因此兩國在此區域未來將趨於競爭關係。 / The tension caused by the South China Sea dispute has been rising in recent years. China has listed the South China Sea as her “core interest”, while the U.S. considers the South China Sea as “national interest”. This, shows that both China and the U.S. have been acting aggressively on the South China Sea issue. Both sides, under their own strategic frames in dealing with the issues, square off over each other’s diplomatic and military acts. Diplomatically, China practices “Good Neighboring Diplomacy” to stabilize the relations with her surrounding neighbors, while the U.S. applies “Forward-Deployed Diplomacy” to bring together each country in East Asia to fight against China. The two countries value the attitude of the ASEAN members more than ever, and this is also the main focus of their diplomatic strategies; both desire to have more say on the South China Sea issue by gaining support from members of the ASEAN. In terms of military operation, China practices “Anti-Access/Area-Denial” to prevent other countries from intervening her sovereignty issues, while the U.S. crafts “Air-Sea Battle”, in which the U.S. applies her devastating military and technology power, and combines the force of each ally to rein China’s military operation. All in all, with the China-U.S. competition as the backdrop, and by referring to John Mearsheimer’s offensive realism, this study examines the future Sino-American relations in the South China Sea. China, as a potential hegemon, possesses a large population and a fast-growing economy; the state also conducts military operations in the South China Sea, with a view to consolidating the mutual economic and trade dependence of China and the ASEAN, even countries in East Asia. Moreover, China excludes the U.S. from dealing with tasks in Asia for the purpose of replacing the U.S. as the Asia’s key player. China’s intransigency in the South China Sea particularly reveals her dominance in the region. Besides, in facing China’s rise in all aspects, the U.S., as the current hegemon, plays the role of “The Off-shore Balancer”. By mixing "Buck-Passing" with "Balancing", the U.S. brings together countries involved in the issue such as the members of ASEAN, Japan, and India to collectively rein the power imbalance in the South China Sea, so as to consolidate her dominance. Both China and the U.S. have raised the level of the South China Sea issue, and have scrambled to gain the dominance in the South China Sea. Therefore, in the future, the two countries will become more of two competitors in this region.