The structural zone of the western Pacific margin is the biggest and most complex plate boundary in the earth. Bounded at Taiwan and the Molucca Sea, it can be divided into 3 sections from the north to the south. The north part, from Kurile to Ryukyu, is a typical trench-arc-basin system, and Kurile basin, Japan Sea and Okinawa trough constitute back arc basin. The central part, the Philippine structural zone, is characterized by complex double subduction. It underwent large displacement and reconstruction in Cenozoic and resulted in much debate for the origin of the South China Sea, Sulu Sea and Celebes Sea. The south part, the New Guinea-Solomon structural zone, resulted from compression and collision among Pacific, Indian and Eurasian plate, with large amounts of strike and back arc spreading. There are new spreading basins and subducting basins among the structural zones. The Taiwan Island is located at the junction, in which the Eurasian plate was torn. Eurasian plate margin subducted eastward beneath the Philippine arc along Manila Trench in the south, while Philippine Sea plate subducted northeastward beneath Eurasian plate along Ryukyu Trench in the north. Molucca Sea is another junction on the west Pacific margin, in which the oceanic lithosphere plate subducted westward beneath Sangihe arc and eastward beneath Halmahera arc, forming reversal U-shaped double subduction zone. Halmahera arc collided with Sangihe arc due to the almost disappearance of the oceanic plate.