: Objective To establish a simplified mechanical model of L4-5 movable lumbar segment according to the sagittal curve of human spine, and to verify and analyze validity of the model structure. Methods An in vitro measurement device based on the time-of-flight (ToF) distance measurement principle was used to obtain the sagittal curve of human spine. Based on the curve, the simplified mechanical model of L4-5 lumbar segment was constructed, and validity of the model was verified from the aspects of range of motion (ROM), intervertebral disc pressure (IDP) and facet joint force (FJF). Results The maximum IDP under 0. 2, 0. 4, 0. 6, 0. 8 and 1 kN follower load (FL) was 0. 23, 0. 46, 0. 69, 0. 92 and 1. 15 MPa, respectively. The ROM of models during flexion, extension, lateral flexion and axial torsion under pure moment were 6. 61°, 4. 03°, 3. 30° and 2. 03°, respectively. The IDPs of models during flexion, extension, lateral flexion and axial torsion under the combined load of FL and moment were 1. 80, 1. 00, 1. 36, 0. 80 MPa, respectively. The FJFs of models during extension, lateral bending and axial rotation were 79. 60, 29. 49, 96. 64 N, respectively. Conclusions The simplified mechanical model based on sagittal curve of human spine can be used for spinal mechanical analysis on changes in sagittal curve of the spine.