Abstract: Coccolith species and percentage analysis for the past 750 ka from ODP Site 1143 of the southern South China Sea has been carried out. The results show that in the mid-Brunhes interval (480~260 ka), the percentage of Florisphaera profunda declined as Gephyrocapsa caribbeanica was booming. Meanwhile, the structure of the sea water has changed, the nutricline depth decreased, and the primary productivity increased. Studies show that during the mid-Brunhes interval, the eccentricity was in a low levels. As the low eccentricity favours the cocoolith growth, it can be detected that the great change in coccolith community is mainly influenced by the eccentricity. Also, the change of the ocean carbon reservoir during the mid-Brunhes interval can be the result of the eccentricity-trigged-booming of the different phytoplankton communities.