To investigate the effect of flex-compression on the stability of lumbar segment movement. Methods: Specimens of thoracolumbar segment (from T12 to L2) were obtained from 7 fresh adult male corpse. Three-dimensional (3D) movement were measured by a 3D spinal motion test machine and stereophotogrammentry before and after the specimens were compressed to failure with a flex-compression load. Results: The results showed that after failure the anterior height and posterior height of the vertebral body were decreasd, and three is a significant effect on the motion of T12-L1, L1-L2 segments in flexion, and L1-L2 segment in left rotation. It has almost no effect on the movement of lateral bending after failure. Conclusion: Lumbar spine lost part of its segmental stability after injury under flex-compression load.