The Cenozoic basalts are widely distributed in the northern margin of the South China Sea. The Early Holocene Shishan Formation basalts crop out in the north of the Hainan Island. These rocks are mainly consisted of olivine basalts. The olivine basalts contain large olivine phenocrysts characterized by high Fo (82. 8～83. 5) and Ni (0. 14%～0. 20%). The studied olivine basalts are enriched in large ion lithophile elements Rb and Ba, and light rare earth elements, as well as high field strength elements Nb, Ta, Zr and Hf, similar to OIB- type rocks. Their mineral compositions and signatures of major and trace elements indicate that the Shishan Formation olivine basalts were generated by low degree partial melting of garnet pyroxenites. The olivine basalts are characterized by homogeneous Sr- Nd- Pb isotopic compositions, which exclude the possibility of significant crustal contamination. Compare with the MORB, the Shishan Formation rocks have higher 87 Sr/86 Sr ratios, lower ε Nd ( t ), and higher 207 Pb/204 Pb (15. 639～15. 643) and 208 Pb/204 Pb (38. 977～38. 996) ratios, which define a mixing trend between a depleted MORB mantle end- member and an enriched mantle component (EMII). Combined with geophysical evidences, we suggest that the depleted mantle originated from the asthenosphere, while the EMII end- member originated from the Hainan mantle plume which contains subducted oceanic crust and sediments. During the ascent of the Hannan plume, the recycled material melted and reacted with the surrounding mantle peridotites in the asthenosphere to form garnet pyroxene. The Shishan Formation olivine basalts were formed after partial melting of garnet pyroxene and crystallization of olivine and minor clinopyroxene. The similarities and differences between the Cenozoic basalts from South China and the Shishan Formation basalts indicate that they had the same end member compositions but were different in the dynamic mechanism, the ratios of different end member and the degrees of partial melting.