Both Taiwan and Japan are located on the intersect of the biggest continent and the biggest ocean of the world. Their strategic positions and geographic locations are inseparable. According to the historical sources, because of the long term communication between Taiwan and Japan, even China's history documents misconceived Taiwan is part of Japan. Besides, after Chin Government subscribing Treaty of Shimonoseki with Japan, Taiwan has formally become the territory of Japan for 51 years. Due to the above reasons, the relation between Taiwan and Japan is intimate. After World War Ⅱ, ROC represented Allies to receive the Pescadores, subsumed Taiwan as its territory without consulting other nations on October 25th, 1945, and repatriated Japanese by a strong hand. In the meanwhile, Japan was occupied by allied forces, neither Taiwan nor Japan had no right to decide their fortune. After recovering the independent status, Japan renounced its right, title and claim to Taiwan, but did not specify to whom the territory was handed over. However, China had been separated into two governments. Under Cold War situation, Japan recognized ROC as China government, on the other hand, keeping the economy relation with PRC by separation of politics and economics to protect its interest. In 1972, Japan Changed the object of reorganization to have the formal diplomatic relation with PRC, but still had stable trade relation with Taiwan. However, after the extreme transformation in Taiwan for almost 36 years, situations have been changed. This thesis mainly observes Taiwan-Japan relation by international law, discusses Japan’s position of the international law status of ROC and PRC, and is intending to offer the future direction of Taiwan-Japan relations.