A system to measure and analyse three-dimensional movements of spine was developed, which is capable of determining the position of points on vertebral and calculating linear and angle displacements of spinal segment. Bilateral facetectomy of cervical spine, as a posterior decompression leading to the instability, must be applied the fusion or the internal fixation to stable the cervical spine. The stable capacity of Halifax Clamp and wire fixation to the instable cervical spine was studied in order to choose an suitable fixation in clinic. On nine fresh adult cervical spinal specimens (C 3-T1), the three-dimensional motions of C4-5 segment were analysed to evaluate the immediate stability following bilateral facetectomy, Halifax Clamp and wire fixation.The results showed that the stability with Halifax Clamp was greater than that of the intact state in flexion, extension and lateral bending, but the same asin axial rotation. The stability with wire fixation was greater and equal to inflexion and in extension,lateral bending and axial rotation respectively. The ROMs with Halifax Clamp were bigger than those with wire fixation in flexion, extension and lateral bending, but closed to in axial rotation.