Objective Coflex interspinous stabilization is a kind of device for the treatment of degenerative disc disease.The key of this surgery is the distance between the spinal dura mater and the U-shaped bottom of Coflex.The influence of different insertion depth of Coflex on the transition segment is the focus of our research.This paper aims to evaluate the influence of the distance between the U-shaped bottom of Coflex and the spinal dura mater on the postoperative lumbar stability via in vitro experiment.Methods Six lumbar spine specimens (L1/L5) from fresh adult cadavers were used in this experiment.Each specimen was divided into 6 groups according to the experimental process: intact state group(A), unstable state group (B),10 mm insertion state group (C), 5 mm insertion state group (D), 0 mm insertion state group (E) and fusion group (F).The movement tests of lumbar specimen were performed under conditions of flexion and extension, lateral bending, and axial rotation.The movement angle and range of motion (ROM) were employed to analyze the stability of the transition segment.Results With regard to the angle range of transition segment for all testing groups, the order of similarity between group A and other groups was: E>D>C>B>F.The ROM of group E was smaller than that of other groups, and group E was of larger stiffness.Conclusions This indicates that the performance of transition segment after surgery is closer to the normal spine when the insertion position of Coflex is near the spine during the flexion and extension, lateral bending, and axial rotation.