Objective To establish a simplified mechanical model of the lumbar spine L4-L5 movable segment according to the sagittal curve of the human spine, and to verify and analyze the validity of the structure of the model. Methods An in vitro measurement device based on the time-of-flight distance measurement principle was used to obtain the sagittal curve of the human spine. Based on the curve, a simplified mechanical model of the lumbar spine L4-L5 was constructed and the validity of the model was verified from the range of motion (ROM), intervertebral disc pressure (IDP) and facet joint force (FJF). Results The maximum IDP under the follower load (FL) was 0.23 MPa, 0.46 MPa, 0.69 MPa, 0.92 MPa and 1.15 MPa. The ROM of flexion, extension, lateral flexion and axial torsion of the model under pure moment were 6.61°, 4.03°, 3.30° and 2.03°, the IDP of each working condition under the combined load of FL and moment are 1.80MPa, 1.00MPa, 1.37MPa, 0.80MPa, and the FJF of extension, lateral bending and axial rotation are 79.60N, 29.49N and 96.64N. Conclusion The mechanical simplified model constructed based on the sagittal curve of the human spine can be used to analyze the changes of the sagittal curve of the spine.