Abstract: Based on the elastic theory and on the torsional geometry relationship of a constrained beam, deduced is a constrained torsional model of a single-node 6-degree-of-freedom, and of low-order beam element with warpage and distortion calculation ability, and enriched is the space model of "two-node bilinear interpolation beam element (Bm_ZY)" . Furthermore, the constrained torsional model was established by ZQFEM software, and the influence of section shape and wall thickness on warpage and distortion was studied. The numerical examples verify the correctness of the displacement mode of the beam element, and the numerical analysis also shows that the warpage and distortion effects will significantly increase the torsional stiffness of the cross section of the beam, and that the results of Midas Civil calculations are not continuous.