Abstract: To take the restraint provided to I-girder webs by the flange and the initial imperfection of structure into account,the advantages and disadvantages of the Basler tension field theory and the Rockey tension field theory were discussed based on a comparison between the nonlinear FEM(finite element method) analysis and test results,and the applicable range of these tension field theories was pointed out,i.e.,depth-thickness ratio of web hw/tw≥160.A formula was proposed for the shear buckling coefficient to describe the restraint of the flange,and the proposed formula was used to modify the Basler tension field theory.The modified tension field theory considering the contribution of the flange was applied to predict the shear resistance of webs,showing an excellent accuracy.The research provides a reference for the designs of steel bridges and other steel structures and the emendation of the related norms.