In this paper ,the elastoplasticity collapse of T-shaped Joints subjected to torsional loading is studied by numerical analysis that using the fmite element method. It is focused attention on the maximum torsional moment, and it is changed the geometry parameters of the main tube to investigate the effects of main tube geometries on the torsional collapse behavior. It is found that the maximum torsional moment decreases with approaching the ratio of the width : B/b (B is the width of the main tube, b is the width of the sub tube)=1.0, because the shear deformation of the main tube. It causes shear deformation of the main tube by twisting sub tube . And the shear strain at the specified faces of the sub tube decreases, so the shear stress decreases .Moreover, it is showed a correlation between the maximum torsional moment and amount of the maximum shear deformation of the main tube.