The dominant period of basin formation is defined as the period with the strongest tectonic movements, the largest extent of subsidence and the best development of source rocks. The sedimentary period of the 3rd member (Shasan, E2s3) and 4th member (Shasi, E2s4) of Shahejie Formation is the dominant period for basin formation. There were many episodes of volcanic movements during Cenozoic in Liaohe Depression, forming distribution of volcanic rocks with many series and types, which changes with the tectonic center and has the less strong activity in the earlier stages. The volcanic movements in the dominant period of Liaohe depression are abnormally strong and the appearances of volcanic rocks are frequent. The reservoirs which are altered by structural fractures and the corrosion and dissolution by formation water are favorable for oil and gas accumulation. The superposition in plane and the alternation in profile provide enough provision conditions of oil and gas sources for volcanic rock reservoirs.