Abstract: Based on examining the seismic profiles distributed at the north and south margins of South China Sea，cobined with the tectonic analysis of its adjacent area，the authors pointed out that this region experienced two periods’extensions，i.e. the earlier simple shear and the later pure shear．The simple shear extension mainly occurred in Late Cretaceous-Early Paleogene，related to slab roll back of Pacific plate，decreasing Paleogene Pacific—Eurasia convergence rate and possible preexisting suture zone．Pure shear happened in response to the extensional slab pull forces from south ward subduction of the Paleo-South China Sea beneath Borneo during the Oligocene and Miocene