The Southwest sub- basin, located at the southwest propagating spreading tip of the South China Sea, features an intact conjugated continental margin and a central rift valley. The sub- basin is a key area for studying the deep structure and dynamic mechanisms of the South China Sea. Previous studies have found that the Southwest sub- basin has a narrow ocean- continent transition and is characterized by slow seafloor spreading rate with numerous syn- spreading faults and ambiguous Moho reflections. However, due to different crustal structures being acquired by diverse investigative techniques, the basic scientific issues such as the rift to drift transition pattern, the slow- spreading oceanic crust structure and accretionary process, the rock properties of Longmen seamounts and the genetic mechanism of mantle are still controversial. Geological sampling and a coincident deep seismic reflection/refraction experiment in the SCSs Southwest sub- basin are required to address these problems. To understand the seamounts deep dynamic process, take geological rock samples from the seamount and analyse their age and attributes. Additionally, to obtain the fine crustal structures, high- precision seismic reflection/refraction exploration is carried out in combination with petrophysical analysis, structural imaging, and forward inversion of material composition parameters to achieve crust- mantle scale seismological perspective. These studies will enrich and enhance knowledge about the procedure of continental oceanic transition and the pattern of oceanic crust accretion in the Southwest sub- basin.