This research presents a new approach formula that predicts the flexural behavior of steel cold-formed I-beam with strengthened hollow tubular flanges. Rectangularity aspect ratio and strength of the strengthening material effect on the flexural behavior of steel cold-formed I-beam with strengthened hollow tubular flanges were studied and analyzed. A wide range of investigations was carried to figure out the effect of the hollow flanges rectangularity aspect ratio and its strengthening material. Eighty-eight numerical models were created and analyzed using the finite element technique. Three-dimensional nonlinear finite element models were prepared using eight nodes solid element with three degrees of freedom per node. Material nonlinearity and geometric effects have been considered in the model analysis. A good agreement between the experimental work done by the authors [1] and FE-model results was achieved and presented. The ultimate load values of the strengthened models were presented and compared with non-strengthened models. The increase of rectangularity aspect ratio and strength of the strengthening material lead to an increase in the section capacity of the studied models. Finally, new equations for the values of the section capacity of the strengthened sections were deduced, taking into account the factors described in this study.