Objective:To investigate the changes in cervical curvature relative to the gravity line in cervical kyphosis and to provide better reference for orthopedic treatment. Methods:Measurements were performed on 60 patients with cervical kyphosis in the sagittal view in the standard,hyper flexion,and hyper extension position including∠A-∠B-∠C,and A,B and C were calculated to ascertain the value of the changes during cervical flexion and extension. The apex of the cervical curve was determined to compare changes in the distribution characteristics with 60 normal people as well as the D value. Results:In standard position,∠A was positive and increased from C2 to C7. In hyper extension position,∠A was decreased and the reduction in amplitude decreased from C2 to C7,while in hyper flexion position,∠A increased and the increase in amplitude decreased from C2 to C7. ∠B followed similar patterns of change with a larger mean value. During cervical flexion and extension,change in ∠A of the upper vertebral body(∠D) was almost equal to change in ∠A of the lower vertebral body and change in ∠C between the two vertebral bodies(∠E). The curve apex was mainly distributed between C4 and C5. Conclusion:During cervical flexion and extension movement,the dynamic changes and regularities of cervical kyphosis patients is consistent with normal people. Cervical vertebral body movement is a rotation and displacement based on a central apex in the sagittal plane during dynamic flexion and extension in both cervical kyphosis patients and normal people. The correction of the cervical kyphosis can be carried out from the apex of the cervical spine,which lays a solid theoretical foundation for the correction of the cervical kyphosis.