Flexible roll forming is a new forming process that produces parts with variable cross sections. This forming process is proposed to meet the need in the weight reduction of automobiles. With deep understanding of this process and reasonable simplification, the FEM model of a nine-step flexible roll forming of an ultra-high-strength steel bumper is established. In order to analyze the mechanics and the deformation characteristics of the flexible roll forming, equivalent stress, equivalent strain, sheet thickness and springback amount are extracted from the simulation result and studied comparatively, which is of great importance to understand the appearance of the forming defects. In addition, the forming load and torque of the rollers can also be obtained which can guide the design of the flexible roll forming product line.