The stress field of paleotectonics in the basin can be deduced interms of the combination of the structures and formations, and thencan be simulated in numerical value by finite element method. As known from geologic analysis, Fuxin basin is an asymmetricgraben bounded around by faults and with the basement slightly dip-ping toward east. Its evolution can be divided into two stages. Duringthe middle late period of the first stage, the stress field changedfrom horizontal tenso-dextral shear in early period to horizontalcompresso-sinistral shear in late period. The transformation of stressfield is mainly shown in the change of synsedimentary structural fea-tures, i.e.the structure mainly of normal faults and secondary faulttroughs, extending NE and NNE, in Shahai formation developed in theearly first stage of the basin filling, and the structure chiefly of se-condary en echelon uplift and depression extending NE and NEE inFuxin formation developed in the late first stage. Such transforma-tion of stress field is of common significance for over a hundred faultbasins of same time in north-east China The parameters of the numerical value simulation of the stressfield in Fuxin basin are selected by: 1 )the determination of theelastic modulus and Poissonts ratio of the medium determined by thetest data in the laboratory at the same time with the finding out ofthe distribution of rocks in the basin; 2)the deduction of the regimeof the stress distribution and the function and direction of the exter-nal force within the basin, using the results of analyses of the syn-sedimentary structures and the statistics of joint fissures; and 3)the determination of the deformation condition of boundaries accor-ding to the actual distribution and behaviour of the basin marginalfaults. When the external force on the boundary has the tension of SE159°/10°↑, and the compress of NW 344°/2°↑, the regime of the mar-g inal faults on the east and west sides will be of horizontal tenso-dexlral shear and horizontal compressosinistral shear. The regime ofthe stress, shown by the results of the computation of the two exter-hal forces, is concerted with the synsedimentary structures of Shahaiformation and Fuxin formation in Fuxin basin. The result of geologicanalyses is further confirmed here. The results of numerical value simulation of the tectonic stressfield in two stages are shown by the major stress trace map, the shearfracture map and the regime of the relative values of the main stress.They have well explained the distribution pattern of different fea-tures of synsedimentary structures in two stages