Objective To develop an accurate finite element (FE) model of human L1-S1 spine segment for investigating the pathology of annulus fibrosus rupture of L4-5. Methods Based on CT images of a healthy adult, three-dimensional (3D) model of vertebras and intervertebral discs of lumbar L15 and sacral S1 segment was reconstructed by Mimics 10.01 and Geomagic 10.0 software. The 3D model was then imported into Hypermesh for meshing. With adding various ligaments and assigning material properties of all components, the FE model of L1-S1 segment was established to investigate its biomechanical responses under various loading conditions including axial compression, flexion, lateral bending and extension. Results The global stiffness of the model under flexion, lateral bending, extension with 10 N?m load was 0.61, 0.7 and 0.75 N?m/(°), respectively, which was in good agreement with the experimental results. The strain of annulus fibrosus between L4 and L5 was higher under axial compressive force and bending moment；annulus fibrosus showed obviously stress concentration under any of the different loads. Conclusions The stress concentration and higher strain in annulus fibrosus between L4 and L5 could be one of the reasons leading to rupture. The developed 3D FE model of L1~S1 motion segment demonstrated to be effective in reflecting the biomechanical response of spine and could be used for further spine biomechanics study.