Abstract: There are different deformation characteristics between the east and west part of the number 1 fault in the northern margin of South China Sea(SCS). The east part includes the Beibuwan basin, Qiongdongnan basin, Zhujiangkou basin and Taixi basin, with NE-EW strike segment of normal faults and traverse fold. The west part includes Yinggehai basin, with NW strike transtensiona1 faults. Based on with the features of magmatics, subsidence, sedimentary fill, crust structure in the northern margin of SCS, the authors believe that the east part margin exist three relative tectonic active periods, i.e. 40—50, 28—30, 10—5Ma. They exhibited different dynamics characteristic respectively．The former two episodes are related to the break up processing of SCS. The third is nothing to do with it. The magmatics at the northern margin of SCS are not the correspond activity with the rifting of SCS. Therefore, the east part of the northern margin of SCS belongs to the non-volcanic passive margin according to its forming mechanism. The active factors are overlapped by the interaction of surrounding plates. The west part may be related to the collision of India-Tibet and it is not a part of the northern margin based on the formation mechanism.