The official signing of RCEP in 2020 marks the formal birth of the world’s largest Free Trade Area（FTA）. Japan’s rising economic demand for China under the spread of COVID-19，ASEAN’s firm attitude towards signing the agreement within this year，Biden’s winning in the U.S. presidential election and other factors together make Japan determined to join RCEP agreement，despite that it is difficult for India to return to the agreement in the short term. RCEP is the first agreement signed by China and Japan on mutual tariff reduction and market opening，which not only deepens China-Japan bilateral economic relationship，but also creates opportunities for economic cooperation in Asia-Pacific region as well as the promotion of the industrial chains and supply chains for both countries. However，Japan’s economic diplomacy towards China will remain in a situation of both cooperating with China and competing China in terms of striving for the economic domination in Asia-Pacific FTA and discourse power in international trade negotiation.