Objective To investigate the cl inical appl ication and efficacy of lumbar vertebral canal expansion withpreservation of posterior l igaments complex, and to study its biomechanical properties. Methods Eight fresh lumbosacralcadaveric samples were divided into 3 groups. In group A, 8 intact lumbosacral cadaveric samples were used for biomechanical test. In group B, L3-5 laminectomy were, after the test in group A, performed and the posterior l igaments complex was preserved. In group C, the posterior l iagments complex was excised after the test in group B. In all 3 groups, the axial compression test, three-point bending test and torsional test were conducted. From June 2000 to June 2006, 309 patients (152 males and 157 females, aged 20-80 years with the average of 57.2 ) with lumbar canal stenosis received operation of the lumbar vertebral canal expansion with preservation of posterior l igaments complex. The course of disease was 3 months to 41 years. There were 55 patients suffering from pure lumbar canal stenosis, and 254 from lumbar canal stenosis combined with lumbar disc herniation, among which 105 were at L4, 5 level, 56 at L4-S1 level, 86 at L5, S1 level, and 7 at L2, 3 level. The therapeutic effect was assessed based on the JOA low back pain scoring system, the satisfaction degree of patient and radiographical observation. Results The axial compression test was performed. In the position of forward bending, stress, strain and axial displacement were smaller in groups A, B than those in group C, and axial stiffness in groups A, B was higher than those in group C, and the difference was significant(P lt; 0.01). In the position of backward extension, there was no significant difference among 3 groups (P gt; 0.05). Concerning the three-point bending test, under the same bending moment, there was a significant difference in deflection, dip and bending rigidity between group A and group C, and also between group B and group C (P lt; 0.01), but no significant difference between group A and group B (P gt; 0.05). In the torsional test, under the same torsional angle, the torque in group B was bigger than that in group C (P lt; 0.01). Under the same torque, the torsional angle in group B was smaller than that in group C (P lt; 0.01), and the torsional stiffness in group B was higher than that in group C (P lt; 0.01). The compl ications included 7 cases of distraction of nerve root, 5 leakage of cerebrospinal fluid and 4 wound infection. All compl ications were treated and restored completely. All patients were followed up for 1-7 years. According to the JOA low back pain scoring system, the improvement rate averaged 86.0%. Of all the 309 cases, 163 were excellent, 112 good, 34 fair, and the choiceness rate was 89%. The satisfaction rate of patient was 87%. There was no radiographic vertebral instabil ity postoperatively. Conclusion The lumbar vertebral canal expansion with preservation of posterior l igaments complex is conducive to maintaining the stabil ity of lumbar spine and have good cl inical outcomes.