Abstract: Based on the equilibrium conditions in the axial direction between two adjacent sections of the beam, the calculation formulas are derived for the shear stress perpendicular to the shear force at the junction of the flange and the web of the I-shaped thin-walled beam and the shear stress parallel to the shear force on the flange. It is shown that the obtained results completely satisfy the cross-section symmetry condition and the stress boundary condition. On this basis, a new shear stress distribution diagram on the section of the I-shaped thin-walled beam is obtained. The results of this research can be used as a sample for students to comprehensively study the bending shear stress on I-shaped thin-walled beams.