Objective To evaluation the biomechanical changes on the vertebral body、annuli fibrosis and faced joint of the adjacent segments on the condition of anterior cervical discectomy and plant fixation. Method To measure five cervical spine specimens scope of dimensional and variety of stress on 3 conditions: normal, single segment plant fixation and double segment plant fixation. Each group was measured under the loading of states of vertical compression, flexion, extension and lateral bending. Result After anterior cervical discectomy and plant fixation, at the adjacent segment, the stress、displacement increased significantly except the state of flexion (P<0.05). When the double segment plant fixation compared with the single segment, there was no statistical differences. Conclusion Anterior cervical discectomy and plant fixation can improve the stress and displacement significantly at the adjacent segments, maximum at the state of extension. But there was no statistical differences of the segment selection.