Abstract: Fault plays an important role in petroleum exploration, especially the fault sealing ability which is the key during the formation of the reservoir. The research analysis the controlling factors on fault sealing ability based on the throw, fault filling and fault section pressure. Throw controls the fault types by influencing the contact status of the sand stratum in both sides of the fault; Fault filling decides the sealing ability on vertical and lateral directions and it is also the key of the membrane sealing in lateral fault seal. The pressure on the fault section controls the vertical sealing ability directly, which means the higher the pressure is, the stronger the sealing ability is.