Abstract: The need for straighter bar products continues to increase with the development of production automation technologies and increasing user requirements, and bar manufacturers have set higher requirements for the bar finishing process. The two-roll straightening machine has become the key equipment of the bar finishing line, and its process directly relates to the quality of the final product. The traditional bar straightening technology is based on the theory of primary bending of bars, and by controlling the degree of plastic deformation, the straightening process of bars can be roughly established, but this is not suitable for high-precision straightening. In this study, to obtain the variation law of each curvature in the cross-roll straightening process of bars, a one-time bendingspring calculation model of the bar was realized by applying the spring back theory of small curvature plane bending and the bendingspring back curvature equation. Based on the principle of bending once per half rotation and by considering the residual curvature of the last bending as the original curvature of the next bending, the bending-spring model of the whole two-bar straightening process was established. The evolution of the original curvature, bending curvature, spring curvature, and residual curvature of the whole straightening process were obtained, and then the final residual curvature of the bar was obtained. The theoretical model was used to calculate the production process, and the results are consistent with the field results, which verifies the correctness of the theoretical model. Based on the established theoretical model, the straightening process was analyzed under different diameters, different material yield strengths, and different original deflections, and the deformation law of straightening process under different incoming parameters was obtained. The model can provide a theoretical basis for the optimization design and process parameter calculation of the two-roll straightening machine.