Abstract: In some oil - bearing basins of China, the abnormal pressures do not develop, for example the oil - bearing formation of Tertiary in Liaohe Basin and the Jurassic coal measure in Tuba Basin, which are characterized by the near - hydrostatic pressure. Faults and fractures are the main paths of oil and gas migration, and tectonic stress is the principle dynamics of producing faults and fractures. The writer applies graphs of Mohr's stress circle and failure envelope to discuss this mechanism.According to the abnormal records of ground water table and oil - gas production before, at end after the time of strong earthquake in Eastern China during the latest 30 years, the author indicates that the oil - gas migration along the faults is closely related to the seismic pumping mechanism. The active fault leads to the stress relaxation in faults. especially in its upper part, and then the fluid now from the surrounding rocks towards fault. Based on the fluid potential difference between upper and lower part in fault and buoyance, the oil - gas- water may move periodically and gush out in a mixed phase.