Abstract: Analysis of data from deep well drilling and seismic survey carried out in the Liaohe oil field during the last decade indicates that the pre-Tertiary basement of the region is divided into three blocks running in an EW direction with two faults lying between. On the basis of the differences between the three basement blocks, the location of these faults running through the Liaohe fault-depression is proposed as well as the character of phorogenesis. According to the author, the fault on the east is the main fault, with the one on the west parallel to it. The differences of their occurrence and activities that evidently had played a controlling role in the oil region during Paleogene resulted in the difference of oil accumulations in the eastern and western parts of the Liaohe fault depression.