Abstract: Urxun-Beier depression in Hailaer Basin is the Mesozoic-Cenozoic basin located in the Paleozoic orogenic belt in Inner Mongolia-Daxing’anling area. Based on the sequence stratigraphic theory and sporopollen assemblages, stratigraphic sequences of the Lower Cretaceous have been recognized from bottom to up as: Xing’anling Group, Tongbomiao Formation, Nantun Formation, Damoguaihe Formation, Yimin Formation. The four structural belts with different directions are found in the area. The faults with NE, NEE and NS trends formed earlier with longterm activity, and control on the basin evolution; the faults with NW trend formed later and overprinted on the early structures. The structures of the area experienced four deformation stages in the Cretaceous period, which controlled on the migration, accumulation and distribution of oil and gas, and the later structures destroyed or reformed the earlier oil and gas accumulation. The unconformity within the area is an important migration pathway and good reservoir of oil and gas. The four structural belts with different trends and unconformities are the favorable zones for oil and gas accumulation in Urxun-Beier depression.

Key words: stratigraphic sequence, structural feature, rule of oil and gas accumulation, Urxun-Beier depression, Hailaer Basin