H-beams are currently the largest output section steel in the world. Straightening is an important finishing step in the manufacturing process and directly determines the ultimate straightness of the beams. To analyse the straightening process, a multiroller straightening analytical model of an H-beam was established and is based on the pure bending springback equation of the symmetrical section curved beam. The purpose of the establishment of the model is to calculate the exit residual deflection by inputting the reduction rules and ultimately get the best reduction rules. In the model, the concept of plastic region ratio is proposed. The larger are the plastic region ratios, the easier are the initial curvatures unified, and the fewer straightening roller systems are required, however the greater is the residual stresses. Another innovation of this paper is the definition of a cosine function to express the relationship between reduction and curvature. The function of curvature, which plays an important role in the analytical model, was developed by a large number of finite element simulation and numerical fittings. The principle of the multiroller straightening process is clearly reflected by the analytical model in the theoretical analysis. By contrast, the theoretical calculation results of the analytical model are consistent with the finite element simulation results and the field data. It is suggested that the multiroller straightening analytical model of an H-beam is a theoretical foundation to optimise the straightener parameters and the reduction rules with higher accuracy.