Typically, during the elastic phase of bridge structures, the influence of shear deformation is often disregarded. However, when inclined cracks appear in the web, the shear stiffness experiences a significant decrease, resulting in a considerable contribution of shear deformation to the overall deformation. Therefore, this study investigates the effect of inclined cracks in the web on shear deformation in bridge structures. A theoretical model considering the degradation of shear stiffness due to the development of inclined cracks in the web is proposed. Furthermore, the formula for shear stiffness after the web cracking is derived based on the truss analogy method. Finally, an evaluation process and methodology for assessing the shear stiffness and deformation of concrete girders considering inclined cracks in the web are presented, and the prediction accuracy of this evaluation method is validated through experimental study.