Abstract: Practical production data showed that there are eight types of fault sealing forms and three kinds of sealing mechanisms i.e.fault surface sealing, opposite side rock layer sealing and pressure sealing of pore fluid.The effect of fault activity on oil/gas accumulation existed in two sides :① syngenetic normal fault in active stage acted as flow passageway, ② junction mode of opposite sides changed.Based on study of faults in several major oilfields in the sag, it is showed that sealing capacity and characteristics are related with fault size, junction mode of opposite sides occurrence, burial depth, fluid property and fault activety etc..

Key words: Biyang sag, Fault, Fault throw, Attitude, Oil and gas migration, Oil and gas accumulation, Fault trap