Abstract: The stress property within and near a fault is an important factor of controlling fault seal. In this paper the FLAC-2D finity difference program is used to simulate stress distribution in fault zone and stress variety with depth quantitatively. The results of the calculating simulation show that under the condition of trapezoid horizontal stress and vertical load, the fault seal character could be classified into three sections after depth: in shallow section fault zone is in stress relaxation and open to geological liquids, fault zone is in stress concentration and well sealed in deep section, and a transition section exists between the above two sections. The stress seal model of fault has been supported by data of the sound wave time-difference from oilfield.