Abstract: The tectonic dynamic setting in the south border of Junggar Basin has been generally considered as a Mesozoic- Cenozoic compressive basin. In the discussion of tectonic evolution and structural deformation, only compressive regime and compressive structure were considered, whereas the extensional situation and structure were ignored. In this paper, based on field survey al analysis of former materials, it proposed that the tectonic dynamic regime of the south border of Junggar Basin should be extensional setting during Mesozoic and even a long period of Cenozoic era-it did not become a compressive setting until late Cenozoic era. Six aspects about this viewpoint are demonstrated. Finally, combining with the peak period of oil-generating, it is found that extensional structures (fault block, syndepositional anticlines)were important for capturing early stage oil and gas, and the Mesozoic extensional structures and later inversion structures should be considered attentively in future study of gas- oil structural traps.