Abstract: The south margin of Nansha microblock and Kalimantan-Palawan block was taken as a whole to discuss its structural evolvement during Cenozoic. Through describing the distributions and lithologic characters of ophiolite-melange and magmatic rocks along southern structural boundary of the South China Sea, and analyzing the structural-sedimentary characters of foreland basins in the south of the South China Sea, we found that the forming of those foreland basins was gradually from southwest to northeast, and it started in late Eocene in the southwest and in middle Miocene in the northeast, corresponding to the forming of subduction zone along the south margin. We suggested that in Tertiary the south margin of Nansha microblock and Kalimantan-Palawan block experienced a successive evolving process which was closely linked with the die-out of proto-South China Sea.