Abstract: Roll forming has been widely used to manufacture long channels with complex cross-sections. End flare, one of the typical shape errors, seriously affects the forming accuracy of roll-formed parts, especially using advanced high-strength steel. In this paper, the mechanism of end flare during the roll forming process of a high-strength automobile seat rail is analyzed. The roll forming process of an actual seat rail is designed. The finite element models of the roll forming process and cut-off springback are established to predict the deformation process and occurrence of end flare. Simulation results indicate that the uneven distribution of longitudinal and shear residual stress along the length of the part is the main reason for the end flare. Based on the simulation, two strategies are proposed to mitigate the end flare. Employing multiple bending processes in the transverse direction effectively balances the longitudinal and shear residual stress. Additionally, the longitudinal bending process can make the longitudinal residual stress in the roll-formed parts more homogenised. Finally, verification experiments are carried out, and the forming accuracy of the seat rail is significantly improved.