In this paper, the present structural stress field of T40 reflection layer, the mechanic characteristics and structural active patterns of the second-level fault at the boundary of sub-depression and the third-and forth-level faults within sub-depression in Haian depression were analyzed. The direction of the present maximum principal stress is about NE 70°. The present maximum principal stress is about 50 MPa and the present minimum principal stress is about 30 MPa. By the present structural stress field finite element numerical modeling, we found that the second-level faults at the boundary of sub-depression are characteristic of tensile activity or tensile-shear activity which is in both clockwise and counter-clockwise, and that the activity features vary along the different part of a fault. The third-and forth-level faults within sub-depression have the same activity features as the second-level faults. In addition, some third-and forth-level faults also have compressive or compressive-shearing activity features.