In order to r'eveal the effect of debriding posterior cervical ligaments on the mechanical stability of cervical spines, we performed this experiment in which four cervicalspines of fresh human cadervers were studied(C2-T1). By simulating the normal physical actions of human neck, such as flexion, extension.Sone mechanical were tested before and after removing the posterior cervical ligament elements(the supraspinous ligaments and the interspinous ligaments). The results showed that the compressive stiffness of cervical vertebrae decereased greatly after removing the posterior ligaments, while the strains of which increased abnormally. In contrast to intactstate there were significant difference(p<0.01). At the same time, the total displacements of cervical spines enlarged markedly while vertical compressive stiffness of cervical spines lessend, there were significant differences in comparison with intactspecimens(p＜0.01). After incision of the ligaments the slantangle of cervical spines enhanced gradually, the increments were significant, especially. In the flexion state (p＜0.01). Conclusion: The mechanical stability of cervical spine reduce after depriving of posterior cervical ligaments. If the figments were injuried, either acute or chronic instability would occur.