Abstract: To investigate characteristics and formation mechanism of transtentional structures developed in Linnan subsag of the Bohai Bay basin, more than 30 3-D seismic sections have been interpreted, temporal and spatial distributions of extension rates have been estimated and analyzed, and the planar distribution of faults in three stages, Es3-Es1, Ed and Ng-Nm, have been plotted.2-D linear elastic numerical models have been established to simulate the stress field of the above mentioned three stages, using finite element software FEPG.The results reveal that, the maximum principal stress and maximum shear stress in the northeast of Linnan subsag are larger than those in the southwest; from Es3 to Nm, all the maximum principal stress and maximum shear stress decrease gradually; the shear stresses are larger than tensile ones on the boundary of numerical model at all the three stages, while the ratio of shear to tensile stress increases gradually.Through the study, dynamical mechanism of tense-shearing structure developed in Linnan subsag can be quantified, which is helpful to study the time and ways of Tanlu fault and Lanliao fault effects on Huimin depression or even on Bohai Bay basin.