Abstract: The research of surface water temperature of paleo-oceans is usually focused on Quaternary, rarely earlier than 2.5Ma. Based on the data obtained from sites 1147 and 1148 of ODP 184 Cruise, using long-chain alkenones and oxygen isotopes of benthic foraminifera as proxies, we calculated the marine oxygen isotope composition and the seawater temperature changes since 16Ma in this paper. The planktonic foraminifera oxygen isotope method was adopted to explore the mechanism of ancient seawater temperature change. The results show that the trends of water temperature change in the northern South China Sea kept step with the global climate changes. During the formation of the northern hemispheric ice sheets, the sea surface temperatures are changed synchronously with the benthic foraminiferal δ¹⁸O, which indicate the size of the high-latitude ice sheet. It shows the special nature of ancient climate changes in such a tropical sea as the South China Sea and provides new evidence for the further study of the ancient global climate change in the low-latitude tropical sea.