Abstract: In this paper the additional stress distribution of the locked region and its nearby area in the deep fault under an applied stress field has been calculated using 3-dimension finite element method in order to simulate the action of an earthquake focus to the block on both side of the fault in the course of an earthquake development. The results have shown that the stress concentration in the locked region is remarkable and their values can be hundreds times greater than that in unlocked region in the fault. The values of the principal stresses, the values of the normal and shear stress on the fault plane and the directions of principal stresses in end of locked region are greatly different from those in faults. Comparing and analysing the additional stress distributions at different depth in the fault, we can find the stress states of shllow and deep layers are different obviously and some regular changes occur with the increase of depth.