The Cangdong sag is a superimposed basin.With the structural and sedimentary characteristics as the background, it has complex source reservoir matching relationship. Controlled by boundary faults and tectonic evolution of the difference in Cangdong sag, it formed the main geological features of "two types, three slopes and one tectonic belt" such as the large inherited slope in the south, central fold belt and two sides of the inversion of the slope in the North. Supplied by the four directions of provenance around the Cangdong sag, the distribution of ten different scale delta lobes are just around the lake. It is difficult to further deepen exploration. Guided by the idea of lithologic stratigraphic reservoir exploration, detailed study has been performed based on the evolution characteristics of Ek2 slope and the mechanism of sand control and reservoir control. According to the research results, 36 exploration wells were deployed and 29 wells were obtained. The success rate of exploratory wells was 80%. Based on this geological understanding, great breakthroughs have been made in the exploration of lithologic oil reservoirs and tight oil deposits in the three slopes. On this basis, sand-control and reservoir-control theory of lithologic reservoir was established, and petroleum accumulation theory of fault basin was perfected. This study has an important guiding significance for oil exploration of the sags rich in oil and gas.