According to the shape of T-S curves, the Kuroshio Watermass of the East China Sea in the region studied in the summer time can be divided into four layers, i.e. four watermasses: (1)the Kuroshio Surface Water, (2)the Kuroshio High-salinity Water,(3) the Subarctic Intermediate Water, and(4)the Okinawa Trough Deep Water,However, in winter, only three watermasses exist, that is to say, the Kuroshio Surface Water is absent. The Kuroshio Surface Water is a mixed water of the Continental Water and the Kuroshio High-salinity Water. It is situated on the west side of the Kuroshio High-Salinity Water. It starts to appear in the region studied in May, most powerful in August, and disappears from this region after November. The maximum thickness is generally less than 75 meters in summer. The Kuroshio High-Salinity Water is the core of the Kuroshio Watermass. it consists mainly of the North Subtropical Water, with a salinity ranging about 34.50-35.02%. This watermass is situated above the 500 metre level. There is a High-Salinity core in this layer, the salinity of which being higher than that of the water upper and lower layers. The depth of the core is generally about 150-200 metres;however in winter, in the north and west of this region the core is sometimes located at sea surface. The main body of the Subarctic Inter mediate Water is the North Pacific Intermediate Water formed in the Subarctic region. The upper and lower boundaries of this watermass are situated at depths about 400-500 and 900-1000 metres respectively. There is a core of low-salinity of about 34.32% in the water. The Okinawa Trough Deep Water originates in the North Pacific Ocean where it is located between 1000 and 1200 metres, but below 1200 metres in this region.