Two recently acquired regional multi-channel seismic profiles across the southern margin, the South China Sea (SCS), are interpreted. One line is crossing the entire Nansha region from the deep oceanic southwest sub-basin of the South China Sea, along the Nansha Islands to close to Borneo, and the other one runs east of the Reed Bank. Based on the interpretations of these profiles, the authors worked out stratigraphic sequences, tectonic structures and extension factors. Five tectonic-stratigraphic units are determined, together with 7 sequence boundaries. Detailed analysis reveal two episode of continent extension separated by a distinct unconformity, which likely correspond with the beginning of sea-floor spreading in the South China Sea.