In recent years，under the influence of the global FTA wave，South Korea and Japan began to promote the FTA step by step，going through from negation to affirmation，then to active promotion，with WTO principles being neglected. Because of their similar domestic industrial structures，South Korea and Japan are both facing great stress from home on the FTA with the United States. To make the FTA realized，South Korea and Japan conducted competitive accelerated development with influence on each other. In the end，South Korea-US FTA came into effect while the Japan-US FTA also took shape gradually within the TPP framework. It remains to be seen whether or not signing the Free Trade Agreement with the United States is a proportional cost-benefit way for South Korea or Japan respectively？There are still a lot of uncertainties. From the perspective of economic diplomacy and on such five dimensions as purpose，implementation conditions，effect，domestic reaction and policy outlook，this article makes a comparative study on South Korea-US and Japan-US FTA policies，providing references for China’s participation in the East Asia integration process.