Abstract:The rock series, rock type and SrNd isotopic characteristics of the Cenozoic v olcanic rocks in the South China Sea are similar to those in the southeast coast of Ch ina. On the basis of the spreading age of the South China Sea, Cenozoic volcanic rocks are divided into three stages: the prespreading stage, the spreading st a ge and the postspreading stage. The characteristics of deep processes in the asthe nosphere and lithosphere are derived from primary magma. The depth to the top of the asthenosphere in the spreading stage and the prespreading stage is shal lo wer than that in the postspreading stage. From the prespreading stage to the s preading stage, the depth to the top of the asthenosphere decreased, while the amou nt of interstitial partial melt increased. The evolution of the primary magma s ho ws a progressive evolution sequence of rifting volcanism and the lithosphe ric spreading velocity became faster. From the spreading stage to the postspre ading stage, the depth to the top of the asthenosphere increased gradually, whi le the amount of interstitial partial melt decreased. The evolution of the prim ary magmas shows a retrogressive evolution sequence of rifting volcanism, an d the lit hospheric spreading velocity decreased gradually. The deep characteristics sh owing Cenozoic volcanism are consistent with the opening and closing of the Sout h China Sea, which gives deep evidence for the formation and evolution of the South China Sea.