Objective To establish the finite element model of scoliosis considering trapezius muscle, and explore the effect of trapezius muscle on mechanical properties of the spine. Methods The finite element models of thoracolumbar vertebrae and sacrum were established, and the validity of the models was verified. Scapula and trapezius muscle units were added, and the mechanical influence of trapezius muscle on various parts of the Lenke 1 scoliosis spine under different working conditions was simulated and analyzed. Results The range of motion (ROM) of the spine-muscle model under lateral flexion was 0. 23% less than that of the spine model, and the axial rotation of the intervertebral disc under rotation was reduced by 0. 078° on average. The stress in soft tissues was more evenly distributed on facet joints, and the stress changes in soft tissues were more stable. Under six working conditions, 87. 5% of the lumbar facet joints had reduced stress. Conclusions Trapezius muscle can improve the spine’ s ability to resist deformation, while it also aligns the stress on the spine with gradual distributions. The less stress on lumbar spine, the more external loads human body can bear. The spinemuscle model established in this study is more practical, with certain reference values in clinic practice