Abstract: The effective torsion section is put forward to reflect the torsion action of the column limb based on the rigiditytheory of transverse torsion member of reinforced concrete flat plate_rectangular column connection and aimed at thecharacteristic of the reinforced concrete flat plate_special_shaped column connection. Because the rigidity of the transversetorsion member is various, the hypothesis is made that the linear torison along transverse torsion member is distributed in twodifferent slant lines. The theory expression of transverse torsion member is derived. By the finite element procedure ANSYS,the effective range of the special_shaped column limb contributed to the torsion rigidity is confirmed and the rigidities oftransverse torsion members are evaluated according to different factors.The analysis result also shows that the height of theeffective column limb is equal to the thickness of the flat plate. The trends of rigidities obtained by the finite element methodagree wellwith those of the theory expression method.The theory expression of transverse torsion member can be applied toequivalent column method to analyze the behavior of reinforced concrete flat plate_special_shaped column structural system.