Aircraft wings usually use I?beams as support structures. However, due to changes of the geometric parameters of the I?beams, theoretical calculations will be affected, and the choice of beam theory will directly affect the calculation results. At present, the existing deflection calculation of I?beams is mainly based on the Euler Bernoulli beam theory, without fully considering the shear deformation during beam bending. Therefore, this article proposes a calculation method for I?beams considering shear effects based on the Timoshenko beam theory, which is used to calculate I?beams affected by concentrated forces. By characterizing the effect of shear deformation on beam deformation, the law of action of shear deformation on the beam was obtained, and the deformation mechanism of shear deformation in the beam was explained. Research has shown that when the I?shaped cantilever beam is within a certain range near the fixed end and the span to height ratio of the beam is less than 5, the influence of shear deformation should be considered in the calculation. The theoretical results of internal force calculation obtained by this method are basically consistent with the results of simulation and electrical measurement method, and can be applied to practical engineering calculation.