Objective To establish the finite element model of scoliosis considering the trapezius muscle, and explore the effect of the trapezius muscle on the 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. Then, scapula and trapezius muscle units were added, and the mechanical influence of the trapezius muscle on various parts of the Lenke 1 scoliosis spine under different working conditions was simulated and analyzed. Results The lateral flexion activity of the spine-muscle model is 0.23% less than that of the spine model, and the axial rotation of the intervertebral disc is reduced by 0.078 on average.The stress in the soft tissue is more evenly distributed on the facet joints, and the stress changes in the soft tissue are more stable.87.5% of the lumbar facet joints had reduced stress under the six operating conditions.Conclusions The trapezius muscle can improve the spine's ability to resist deformation while also aligning the stress on the spine with the gradual distribution. The less stress on the lumbar spine, the more external loads the human body can bear, and the spine-muscle model is more practical, with a certain reference value for clinics.