美日安保體制迄今已超越半世紀，對此議題之相關研究已不勝枚舉，然而，大多數研究卻都只局限於單一理論之應用，鮮少有透過跨層次觀點來予以分析美日安保體制之變遷因素，以至於有不能完整詮釋美日安保體制之變遷因素與以偏概全的情況發生，進而遭致批判脫離社會現況。因此，本文認為在全球化與資訊流通迅速的當下，整合理論之應用已明顯是最能詮釋事務變遷之研究方式，這也是為何本文將採取以區域安全為導向之跨層次觀點分析，來探討美日安保體制為何會有所變遷。但由於是以安全議題為出發點，所以將有別於以往的跨層次分析方式，而是採用一種以國際結構(outside-in)為主軸，並加上國內政治與領導人等(inside-out)之影響因素為輔的研究方式，以避免單一層次研究之侷限性。此外，本文也試圖應用美國評斷日本於美日安保體制中之表現的審核機制，來分析日本從1951年美日安保條約之制定，至迄今間，於美日安保體制中的角色、任務和能力等地位是否有逐漸提升之趨勢？ The Security Treaty Between the United States and Japan was signed on 8 September, 1951. For over 50 years, there are many associated researches on the U.S.-Japan security alliance, yet most of the researchers adapt in only one single theory to study the alliance partnership, instead of a levels-of-analysis approach which could possibly analyze the factors of the change, development and transformation of U.S.-Japan security alliance in a comprehensive perspective.Thus, due to respect of globalization and information transfer efficiency, I believe levels-of-analysis is a proper research approach to interpret and study international affairs in the era of dynamic. This research focuses on why the U.S.-Japan security alliance system changes over time, with a perspective on regional security. Putting the regional security into perspective, the levels-of-analysis approach of this research is slightly different from the usual approach. By taking an outside-in method as the primary factor analizing way and inside-out as a secondary factor analyzing way, I suggest it will be able to avoid the demerits and constraints caused by taking only one single level as a research approach. In addition, I also analyze whether since 1951, Japan’s changing role in the U.S.-Japan security alliance system acceleterate with the RMC assessment.