日本民主黨於2009年上臺後，曾積極改善與北京 的關係，而後者也對此表示歡迎。但兩國間的和緩關 係為時甚短。 本文從權力政治角度切入，認為曰本民主黨試圖 從向華府一邊倒，轉為尋求與華府北京的等距關係， 是意圖增進曰本利益的理性行為。可是原本在東京一 北京一華府戰略三角中，處於左右逢源之樞紐地位的 美國，其相對利得會因此受損。比中國大陸或曰本更 強大的美國，並不樂見東京過於向北京靠攏，所以曰 本民主黨對北京的政策很難突破此一結構限制。

Coming to power in September 2009, the Democratic Party of Japan had started to ameliorate the relation with Beijing actively. However, this policy failed, although China also welcomed it. The detente between Mainland China and Japan was short-lived. From a power politics perspective, this paper argues that the DPJ rationally tried to seek a balance position between the United States of America and the People’s Republic of China to promote Japan’s interest. But this move would damage the USA’s relative gains in the Washing-Beijing-Tokyo strategic triangle. Since the USA is more powerful than Japan or the PRC, it is difficult for the DPJ to overcome this structural limit.