Ordovician interior buried hills here refer in particular to the discovered Ordovician buried hills that are overlaid by Carboniferous-Permian strata in Bohaiwan Basin. Most of the interior buried hills are monoclines in structure and the buried hill reservoirs basically are anisotropic "blockoid textures". The hydrocarbon in Paleogene-predominating source rocks migrated down along the mountain-controlling fault surfaces and accumulated into the Ordovician interior buried hills as a pattern of "source in the upper and reservoir in the lower" or "source late and reservoir old". It is indicated that the factors controlling with hydrocarbon accumulation in the interior buried hills are, in significant extent, the hydrocarbon -generating potential of source rocks, the effective hydrocarbon -supplying window, dominant draining layers and the developing reservoir fractures. Hydrocarbon accumulation may be greatly enriched in scale in interior buried hills if all of four favorable controlling factors are possessed while hydrocarbon accumulation can still take place but may be small in scale if any one of other three controlling factors is not favorable. Fractures are the main reservoir space in interior buried hills and the development of these fractures is controlled by geological structures and faults shapes. Anticlines, arc faults and multidirectional crossing faults are favorable for developing fractures while the fractures controlled by liner faults are not so developed in buried hills.