Objective To evaluate the optimal traction amount for treating scoliosis using halo pelvic ring traction (HPRT) and provide theoretical references for clinical surgical assessment and rehabilitation. Methods A three-dimensional (3D) model of the thoracolumbar spine including the spinal cord was created and validated. Five traction amounts (10, 15, 20, 25, 30 mm) were applied to the model. The biomechanical responses of the spine under different traction conditions were simulated to determine the optimal amount of traction. Results As the traction increased, the Cobb angle decreased progressively. Significantly, in the range of 15–20 mm, the reduction in Cobb angle accounted for 50–70.5% of the maximum reduction. The spinal stress at the main curvature represented 47.4%–67.5% of the maximum stress. Meanwhile, the stresses in the gray and white matter of the spinal cord were 70.3%–84.5% and 68.8%–83.9% of their respective maximum stresses. Conclusions The traction amounts between 15 mm and 20 mm are optimal for treating scoliosis. This range maximizes the Cobb angle correction while maintaining lower stress levels and thereby, reduces the risk of damage to the spine and spinal cord.