Abstract: By means of high-resolution sequence stratigraphy, tectonic stratigraphy, fine sedimentary system analysis and tectonic-palaeogeomorphology recovery, the formation feature and process of the Changling Sag during depressive stage were studied systematically. It was concluded that during the depressive stage, the sag was both uplifted and depressive controlled by multiple circles of slope-break belts. The slope-break belts not only divided geographic units, but also controlled the changes of sedimentary facies, resulting in the close coupling relationship between palaeogeomorphology and sedimentary system distribution. Furthermore, 4 favorable exploration regions in the study area were proposed, including the plain lithofacies of uplift belt, the proximal delta front of slope belt, the proximal delta front of deep depression, and the far delta front of deep depression.