Based on drilling data, seismic data, gravity anomaly and magnetic anomaly, it is revealed that there is symmetrical similarity between Nansha massif and Zhongsha-Xisha massif in crustal structure, gravity anomaly and basement lithology, which are conjugated with the expansion ridge of South China Sea as axis. Under the control of three tectonic events, three unconformity surfaces developed including RU (Rift Unconformity), BU(Breakup Unconformity), and CU(Collision Unconformity), which can be identified on seismic profiles. Then a unified framework with three tectonic layers was setup in the basins of different massifs. According to seismic data, we study the tectonic characteristics of three basins such as Liyue Basin, Beikang Basin, and Nanweixi Basin in Nansha massif. Divided by the CU surface, the structure of these basins show the characteristics of "lower fault and upper depression" on the whole. In the lower tectonic layer (RU-BU), graben developed with faults of different strike such as NE, NEE and NW. In the middle tectonic layer (BU-CU), half-graben or graben developed with sub-faults of EW strike besides the former faults. In the upper tectonic layer (CU- seabed), stable depression developed.