Ocean sciences progressed rapidly in the 20th century, especially during its second half.  At the same time, the important role of the oceans in the sustainable development of human society has also been recognized.  It is suggested that China should pay special attention to two areas in ocean sciences research in the early 21st century.  One is the role of the oceans in the climate variability at the seasonal, interannual and interdecadal time scales.  The other is the response of the coastal systems and marine ecosystems to both natural environment variability and anthropogenic activities, including the global change.  In this paper we discussed the related research topics for China in the early 21st century, after reviewing advances made worldwide in both ocean circulation and marine productivity in the 20th century.