Abstract: Palaeogeomorphological units, such as paleo-bulges, paleo-sags and paleo-valleys, are critical in controlling the formation and development of sedimentary systems and sequences. Sediments move through paleo-valleys (usually structural slope-break zones) and are finally deposited in paleo-sags as fan deltas and/or turbidite fans. Therefore, palaeogeomorphology research can help reveal the spatial distribution of depression and deposition centers for predicting sand-rich sedimentary systems so as to benefit the exploration of oil and gas in petroliferous basins. Balanced cross section has been widely applied in recent years as an efficient tool for study of tectonic evolution. In this paper, we used the balanced cross section technique to reestablish the palaeogeomorphological framework, taking the nose-like structure in Xiagou Formation of Lower Cretaceous in Yaxi area, Qingxi sag as an example, where fan delta, lacustrine and gravity flow depositional systems are well developed. The influence of palaeogeomorphology on sedimentary system was discussed in details.