Abstract: The northern margin of South China Sea, known for its complicated tectonic features, is located at the intersection of the Tethyan and Paleo-Pacific tectonic domains. There are hot debates on its tectonic behavior from an active continental margin to a passive continental margin and from a volcanic passive continental margin to a non-volcanic passive continental margin. Differences are coming from several reasons: ① different models are adopted to study the formation and evolution of the South China Sea; ② the tectonic characteristics of South China Sea margins are diverse; ③ lack of detailed understanding of magmatic activities; ④ constraint of research methods. In order to better understand the tectonic behavior of the north margin of the South China Sea, it is suggested carrying out comparative study with some typical areas in the world, further analyzing the process of formation and evolution of the South China Sea and carrying out Ocean Drilling and multi-disciplinary comprehensive analysis so as to reveal the characteristics of multi-phase expansion of South China Sea and the tectonic attributes of the northern margin. Our initial study shows that the expansion of three sub-basins in SCS is similar to the formation of Trigeminal Rift System. The first phase of sea-floor spreading was mainly driven by tectonic tension and characterized by Non-volcanic passive continental margin, while the second phase sea-floor spreading was driven by upwelling of the mantle and as a result formed was a volcanic passive continental margin.