Objective:To analyze the improvement of patients with basilar invagination and atlantoaxial dislocation that treated by anterior or posterior surgery.Methods:50 patients with basilar invagination and atlantoaxial dislocation that underwent simple anterior or posterior surgery from 2009 to 2021 were included. There were 34 females and 16 males with a mean age of 45.04 years (range, 18-65 years). All patients underwent thin- slice CT scan of the neck. Preoperative and postoperative measurements of atlantoaxial joint distance, atlantoaxial joint angle, atlantoaxial joint displacement, Claus' Height, atlas-dens interval, space available for the cord, cervicomedullary angle, C 0-C 2 angle, and C 2-C 7 angle were measured. Then, the data were analyzed by independent sample t test. Results:25 patients (7 males, 18 females) were included in the anterior surgery group, and 25 patients (9 males, 16 females) were included in the posterior surgery group. The mean age of the two groups was 45.24±9.86 years and 44.72±14.06 years, respectively, showing no statistical difference. The mean last follow-up time of the anterior and posterior surgery group was 6.48±3.14 months and 7.04±2.87 months, respectively. The odontoid distance, atlas-dens interval, space available for the cord and cervicomedullary angle in 2 groups were significantly improved after surgery ( P<0.05), while there were no significant differences in the above parameters between 2 groups ( P>0.05). In the anterior surgery group, the distance and angle of atlantoaxial joint were increased, and the atlantoaxial joint displacement decreased significantly. While in the posterior surgery group, only the atlantoaxial joint space increased ( P<0.05). The C 0-C 2 angle was significantly increased and the C 2-C 7 angle was significantly decreased in the anterior surgery group ( P<0.05), but there was no significant difference in these parameters in the posterior surgery group ( P>0.05). In addition, there was no significant difference in parameters between the two groups at the last follow-up compared with those immediately after surgery. Conclusion:Both anterior and posterior surgery can improve the compression of the spinal cord in patients with basilar invagination and atlantoaxial dislocation. Anterior surgery may be more adequate for the extension and reduction of the atlantoaxial joint space, however, excessive enlargement of the lordosis angle in upper cervical may lead to the reduction of the lordosis in lower cervical.