[Objective] To explore the long-term efficacy of simple posterior fixation in the treatment of free odontoid process with atlantoaxial dislocation [Methods] 29 patients who received simple posterior fixation in our hospital from January 2010 to December 2015 were selected. A case of patients with free ossicles of the odontoid process combined with atlantoaxial dislocation was collected. The preoperative and postoperative imaging data and functional evaluation results were collected, and the long-term efficacy of the patients was statistically analyzed. [Results] The average follow-up of 29 patients was (9.2±2.7) years. The average improvement rate of JOA score after operation was 77.35%, while the excellent and good rate was 100%. The preoperative ADI was (9.23±2.16) mm, C0~C2(1.74±15.28)°, C2~C7(27.34±8.27)°. On the 7th day after the operation, the ADI of the patients had been significantly improved, with statistically significant difference compared with it before the operation (P<0.001). At the last time follow-up, C0~C2 was（14.91±6.36）° and C2~C7 was（19.39±5.21）°,with statistically significant difference compared with preoperative (P<0.05). [Conclusion] Posterior fixation alone can significantly improve atlantoaxial instability, with great long-term follow-up effect. Posterior fixation alone is an effective treatment for free odontoid process combined with atlantoaxial dislocation.