南海主權是目前世界上涉及國家最多範圍最廣，情況最複雜的國際爭端。雖然美國是南海的域外國家，但是，南海情勢的發展關係著美國的核心利益，除了在東南亞地區厚植其戰略資源外，更要確保美國的航行自由，並鞏固自身在亞太地區的霸權位置，更進一步藉此遏制中國日漸上升的地區影響力。 2011年歐巴馬宣布美國新的「重返亞太」戰略，強調將在亞洲地區投入更多的外交、經貿及軍事資源等，對南海問題採取積極干預的態度，逐步將其推向地區化和國際化。因此，南海問題逐漸與美國的亞太政策掛勾，美國行政部門相繼表態，提出插手南海問題的政策聲明。其中，歐巴馬南海戰略的成效取決於其「亞太再平衡」政策。本文主要探討2009到2016年歐巴馬總統任內的美國南海戰略方針與具體作為，著重探討其第一、二任時期南海戰略差異性。 相較於第一任總統任期，在歐巴馬第二任期當中，南海議題的重要性急遽上升。為因應中國在南海的島礁軍事化，歐巴馬政府採取多元手段以施壓北京，其中最引起外界關注之舉，莫過於支持菲律賓採取國際仲裁途徑解決南海問題。之後更強勢要求各方禁用武力，重申以和平手段解決爭端，並呼籲北京當局與國際社會應支持仲裁結果。研究結論如下:(一)美國重視南海資源，介入紛爭導致區域危機升高。(二)美國重返亞洲目標在制約中國力量。 總之，歐巴馬支持周邊南海聲索國經由「聯合國海洋法公約」解決南海主權爭端;並與東協成員國共同合作來遏制中國。中國與美國在南海爭端的較勁，正是兩大強權競合的縮影，再加上中國加速在南海海域軍事化建設、周邊南海主權聲索國無法達成共識，紛爭不斷更是激化南海問題。美國與中國兩大霸權的擴張，必將發生權力衝撞，導致未來美中關係及南海問題的解決增添變數。
The South China Sea sovereignty is the world’s most extensive and most complicated international dispute. Although U.S.is not located in the region of South China Sea, it greatly concerns about its core interests in the region. In addition to strengthen its strategic resources in Southeast Asia, also important to ensure the freedom of navigation of the United States and consolidate its leadership in Asia Pacific. Furthermore, it is also necessary to engage China’s rising influence in the region. In 2011, President Barack Obama declared “Pivot to Asia” and emphasized that the U.S. will enhance more diplomatic, economic, trade and military resources in Asia and implement “Rebalancing toward Asia” strategy. Obama began to intervene within and make it emerging regionalized and internationalized. Therefore, South China Sea dispute is gradually connected with the U.S. Asia-Pacific policy. The U.S. administration has stated its point of view and released its statements about disputes in the South China Sea in public. Obama’s South China Sea strategy depends on “Rebalancing to Asia”. This paper aims at examining U.S. South China Sea strategy under Obama’s administration, especially the differences between Obama’s first and second term. In comparison with Obama’s first term, he drew more attention onto South China Sea disputes in his second term. He adopted diversified measures to cope with China’s military build-up in the South China Sea, especially he supported the Philippines in resolving the South China Seadisputes through international arbitration. Afterwards, he urged claimant countries to solve South China Sea disputes in peace, furthermore, urged Beijing and international community to accept the arbitration result.The conclusion is as follows: First, U.S. values natural resources in the South China sea and regional tension gets higher with U.S. involvement. Secondly, the aim of “Pivot to Asia” policy of U.S.is to suppress China. In sum, Obama encouraged those claimant countries to solve maritime dispute by UNCLOS and U.S. also cooperated with ASEAN members to suppress China. In particular, the competitions between Chian and U.S. in the South China Sea somehow will have more conflicts. In addition, China keeps building up military facilities on South China Sea islands and ASEAN members can’t reach consensus. Due to these elements, the solution to the U.S.-China relations and maritime dispute in the South China Sea would be still unpredictable.