In this paper,from the perspective of international political economics, We analyze the political and economics factors which affect Japan to start FTA process, in order to judge the possibility of Japan to participate in trilateral FTA or TPP. Judging from the traditional revenue, Japan hopes to obtain economic benefits from the rapid economic development in China and South Korea, through the signing of FTA; Judging from the non-traditional revenue, considerations of the dominance, national security and interest groups, Japan has to pay attention to the signing of TPP. If Japan has to make a choice between the two, It may preferentially select TPP. <<