Abstract: Xihu Sag represents the core hydrocarbon exploration target of East China Sea Shelf Basin. The magnitude of erosion caused by Longjing Movement during the late Miocene has long been controversial. As existing research results cannot precisely characterize paleogeomorphology, this paper systematically reconstructs the Miocene paleogeomorphology of the study area. The adjacent-layer thickness ratio method is adopted to calculate stratigraphic erosion, with cross-validation from single-well data to ensure reliability. A petrophysical model was established via the back-stripping method is applied to establish to correct for compaction and restore the original thickness. Finally, by integrating residual thickness, erosion thickness, and compaction effects, the quantitative reconstruction and systematic analysis of the pre-Miocene depositional paleogeomorphology in Xihu Sag were achieved. The results show that erosion primarily occurred in the eastern anticlinal zone, with erosion amounts ranging from 2000 m to 2800 m, significantly greater than the previous estimate of 800 m to 1000 m. The reconstructed Miocene paleogeomorphology exhibits higher elevations on both the eastern and western sides, and generally higher topography in the north than in the south. The basin has a single depocenter, with a northeast-southwest trending zonal structure, steep eastern flank and relatively gentle western slopes. The depocenter is located in the central-northern part of the sag. This study provides a revised estimate of the erosion caused by Longjing Movement and delineates the overall paleogeomorphology framework of the Miocene strata. These findings offer a theoretical basis for understanding the distribution of the Miocene sedimentary facies and predicting sand-body distribution, and offer significant guidance for selecting favorable exploration targets in Xihu Sag.