美日安何不僅是一項兩個當今經濟、政治和軍事強國之間的軍事聯盟，更是兩國共同用以維護亞太地區安全與和平的政策設計與安排機制。從冷戰時期對付蘇聯的威脅，到冷戰後的重新包裝，美日安保是美國亞太安全戰略之中，最為重要的一個環節。本文將從對美日安何條約和指南的條文分析出發，突顯出美日安保體系的演變歷程與爭議重點。其次，文章討論美日安保條約和指南對於亞太安全環境的影響，主要是討論美國在亞太要軍事存在的重要性、日本在維護區域安全方面的新角色與限制、以及美日安保條約和周邊地區的義和安全意涵等爭議。最後，作者進一步指出美日安保體系對於亞太安全環境的重要性與的，在理論層面上兩項重要特徵：集體安全體系下之集體自衛和威脅平衝理論之現狀結合。

　　　　　The U.S.-Japan security alliance is viewed by many leaders in the Asia-Pacific region as the most important stabilizing factor for maintaining security in the region. Though it is a bilateral treaty in its nature, the U.S.-Japan security cooperation has unique impact and importance in regional security environment. The article will address some significant issues security environment. The article will address some significant issues resulted from the newest review in 1997 of the guidelines of the security alliance between he major countries both in the region and international society. The paper first discusses the evolution of the security alliance, form the treaty signed in 1951, revised provisions of 1960, first guidelines of 1978, and the latest review of the guidelines in 1997. From the text analysis for some important provisions and concepts in the forty-year long security cooperation, the paper reveals the major developments of the security alliance. The second part of the paper focuses on three core implications of the U.S.-Japan security alliance for the security environment in the Asia-Pacific. These factors are as follows: the U.S. military presence, the changing role of Japan in security affairs, and the meaning and influence of the "Far East clause" or "areas surrounding Japan" in the document of the security cooperation. The theoretical explanations and implications of the U.S.-Japan security alliance will be discussed in the final part of the paper. The author argues that the bilateral military cooperation between the U.S. and Japan can be regarded as the collective self-defense mechanism under the idea of collective security. Furthermore, the security alliance also can be viewed, from the realist ideas of international security, as the combination of the status-quo countries under the idea of balance of threat to demonstrate their determination to maintain peace and security in the region.