Abstract: The changes in the relations between US and Japan after WWII had been the major element affecting the stability of Eastern Asian region.The focus of United State’s policy towards Japan at the early postwar period of WWII experienced a transition process from transforming to supporting.The transition had a complicated historical background and reason，went through a tortuous transformation process.The direct result set a base for the following USJapan relationship and now has a major effect upon changes in the international political structure of Eastern Asian region.Those elements affected US to change its policy towards Japan in the early years after WWII are not so important as analyzed by those Chinese and foreign scholars，but all of which have a logical connections，some coming first，other following afterwards，or some being primary and other being secondary and finally leading to the formation of the “San Francisco System”.In the process of changes in US policy towards Japan，disputes in ideology and gambles on national interests between US and the Soviet Union interacted honestly and straightforwardly，sometimes agreed with each other，sometimes departed from each other，aiming at their own individual national interests.All of these are important references for predicting the trends of the current international political structure of Eastern Asian region，and for the fundamental key and policies in correctly dealing with international affairs of that region.

Key words: US, Japan, US-Japan Relationship, policy towards Japan, early post-war period of WWII