On the basis of the recently available drilling data and 3D seismic data from Xihu Depression and the reinterpretation results of 2D regional seismic profiles, the activity history of the major boundary-faults are quantitatively analyzed. In vertical, there are three major seismic unconformities including T30 ( the top of Pinghu Fm.), T34 ( the top of Baoshi Fm.) and T24 ( the top of Huagang Fm.) . The scale, the fault development density, and the lateral strata thickness variation of the three unconformities are carefully investigated. The faulting activities and lateral change of strata thickness below and above the three unconformities, the depositional cycles and the intensity of sedimentary facies transition are compared. It is concluded that only the unconformity T30 can serve as the transitional unconformity between the syn-rift and the post-rift depressions. This unconformity T30 is the largest in scale, and demonstrates the largest transitional intensity in structural style, sedimentary facies and fault growth indices below and above the unconformity. By contrast, it is considered that the interface T34 is only a second-order unconformity between two rifting episodes and the interface T24 is only a secondary-order unconformity between two depression episodes in the basin.