Abstract: Based on the conductivity-temperature-depth (CTD) data from the compositive survey in the westen Pacific, the distribution characteristics and change regularity of the temperature, salinity, speed of sound and density in the easterly ocean nearby the second island chain in winter have been analysed. Data were processed with average gridding methods by using a software named Ocean Data View (ODV), and the speed of sound and sound velocity gradient were obtained with the speed calculation method of Wilson and vertical gradient methods. Comprehensive analytic results indicate: the temperature are decrease as the depth increase, and the rate of change is obvious above 750 meters; however, the characteristics of vertical structure of salinity and speed of sound values are decrease first, and then increase downward from surface layer, which have different critical depth. There are two thermoclines in the sea area, the upper one is stronger and thinner than the under one.

Key words: the second island chain, winter, hydrological elements, distribution characteristics