Purpose <p>Halo-pelvic traction (HPT) safely improves spinal deformities by applying continuous, controlled axial traction between the skull and pelvis, creating favorable conditions for subsequent surgery. The regional mechanical relationship between spinal stress and improvement of vertebral axial rotation in severe rigid idiopathic scoliosis with HPT was clarified in this study.</p> Methods <p>A finite element (FE) model of C3–S1 spine was constructed to simulate three displacement conditions of HPT (5&#xa0;cm, 10&#xa0;cm, 15&#xa0;cm). The regional mechanical relationship between spinal stress and the improvement of vertebral rotation was clarified.</p> Results <p>Vertebral body rotation improvement ratio, cortical/cancellous stress ratio, bilateral facet joint cartilage stress ratio were highly constant under traction displacement of 5&#xa0;cm, 10&#xa0;cm and 15&#xa0;cm. The junctional area (T4–T5) achieves the most efficient vertebral body axial rotation improvement with moderate cortical/cancellous stress relief, high disc stress drive, and extreme asymmetry between left and right joints. The main thoracic curve apex T9 has a high cortical/cancellous ratio due to extremely low cancellous bone stress, a decrease in disc stress, and high bilateral facet joint stress, and a very low rotation improvement. Cortical overload was observed at T7 adjacent to the main thoracic curve, but there was still significant rotation improvement. Cortical/cancellous coordination was observed at upper thoracic curve apex T2, and axial rotation was significantly improved. Cortical/cancellous simultaneous unloading was observed at lumbar curve apex L2, and axial rotation was extremely low.</p> Conclusions <p>Vertebral body axial rotation improvement in severe rigid idiopathic scoliosis with HPT was dominated by regional mechanical matching.</p>