A biogenic silica analysis was performed on 857 samples at ODP Site 1144 in the northern South China Sea. The correlation of opal content and MAR with oxygen isotopic records of plankton foraminifera shows that they increased during glacial periods and decreased during interglacial. The increases of opal content and MAR after the middle Pleistocene (about 0. 9 Ma) result from the higher surface productivity, which was induced by the intensified monsoon circulation after the " Mid ?Pleistocene Revolution" and the special situation of Site 1144. The time ?sequence spectral analyses of oxygen isotopic record, opal content and MAR reveal that the variability of the surface productivity were dominantly forced by the earth orbital cycles.