The three-point bending pressure straightening method is employed to deal with the problem of single curvature bent stepped pipe. Based on the theory of elastoplastic mechanics the analysis of deformation process for the stepped pipe with bilinear strengthening elastoplastic material is performed,in which the effect of stress concentration at the changed cross-section place is considered. Therefore,the calculation formula of straightness stroke is deduced. The correction of the mathematical model is verified by the straightening process simulation based FEM analysis of explicit dynamics in Workbench LS-Dyna software and the corresponding experiment. The simulation and experiment results show that stepped pipe rectified by the proposed method has high straightness,meaning a good straightening affect.