Abstract: The structures of the Xihu Sag in the rifting stage include those formed from the onset of rifting(boundary Tg) up to the Late Eocene(Boundary T 30)in this paper.The Structural pattern is the factor controlling over the development of stratigraphy and the spatial distribution of depositional systems.The prototype of the basin during the rifting stage is a complicated half graben controlled by three groups of fault zone,i.e.the fault zone on east steep slope,the fault zone in central depression,and the fault zone on west gentle slope,all extending in NE direction. The plaeo-structural pattern of the Xihu Sag during the rifting stage plays significant roles in the formation of sedimentary sequences,and the distribution and shifting of depositional and subsidence centers. The sedimentation and tectonic events are episodic as a local response to the subduction of the Pacific plate under the Eurasian plate starting from the late Mesozoic.