Abstract: For the obvious neutral layer offset of a large cross-section bar in the two-roll straightening process,which has large impact on the roller type and the bar straightness accuracy,a neutral layer offset model was established based on the three-point bending and elastic-plastic theory. Combined with room temperature tensile test and bending test,the neutral layer migration regularity was studied in the bar straightening process. It is found that the influences of the bending radius and mechanical properties of the bar on the neutral layer offset are obvious. The smaller the bending radius is,the larger the neutral layer offset is. The neutral layer offset for low strength and strong plastic materials is larger. The reliability and applicability of the model are verified by bending test.