Abstract: Under eccentric loads, the torsional effects of steel-concrete composite spine girder with long flanges supported by cantilever beams with corrugated webs (SCCSG) are significant. An analytical model and a calculation method are proposed in this study, which are based on the Second Theory of A.A.Umanskii for the torsional behaviors of the SCCSG structure considering the influence of the cantilever flanges. The theoretical calculation method is verified through an experimental test and spatial finite element (FEM) analysis. The comparison of results from theory, test and FEM indicates that the analytical model and theoretical method can generate conservative results satisfying design requirement. The further investigation shows that 1) The warping stress and the additional torsion shear stress of the SCCSG structure contribute a large proportion of the total flexural stress, and should be taken into account in engineering design; 2) It is more reasonable to consider the influence of cantilever flanges for torsion analysis; 3) Single-point twist moment should be used as loading pattern for torsion checking of structural design; 4) The distortional stresses of composite spine girder are negligible.