Abstract: The west tropical Pacific is the most vigorous one among global ocean-atmosphere interaction areas, as a significant part of Earth's climate system. To obtain the Sea Surface Temperature (SST) variation during the Last Glacial maximum (LGM) in this area, a gravity core WP7 from Ontong-Java plateau and some other cores were chosen. By solving the equations consisting of G.ruber's shell Mg/Ca, oxygen isotopes (δ¹⁸O_c) and SST, the impact upon G.ruber's shell Mg/Ca brought by seawater salinity was eliminated and SST estimation was obtained. The result shows that SST at west tropical Pacific is about 4.5℃ lower during LGM than in Late Holocene, and in the heart area of West Pacific Warm Pool(where modern SST is higher than 29℃) is about 3.9℃, smaller than 5.8℃ of the tropical Indian Ocean, and close to the figure of 3.6℃ in the east tropical Pacific, which may be the result of eastward migration and shrinking of West Pacific Warm Pool.