Abstract: Objective: The pathology and orthodontic mechanism of adolescent idiopathic scoliosis are always concerned by scholars and experts of medical profession and engineering community. The structure of spine is complex, and the establishment of the spine model is more difficult. With the combination of mechanical thoughts, spine biomechanics and medicine, one new modeling method which is fast and effective was explored. The effectiveness of this method was verified in the paper. Methods: The vertebra, intervertebral discs, small joint of spinal were regarded as the mechanical parts in the study. According to the data which is provided by literature and medical school, the models was established and they were combined into a whole in the light of certain assembly relation. Then the simplified model was imported into ANSYS and the finite element model of L1～L5 segment lumbar was established. Results: The 3D simplified geometry model of L1～L5 section lumbar was established by the mechanical methods and its effectiveness was verified in this paper. Conclusion: The simplified model of L1～L5 section lumbar which was built by mechanical method was effective. The model was similar to the real spinal. The critical sizes, mutual connection relationship and sports relationship were grasped accurately. The modeling cycle was short and it could be modified conveniently. It is hoped that this modeling method can provide some convenience for exploring the etiology and pathology of adolescent idiopathic scoliosis in future.