【Abstract】 Objective To determine the three-dimensional stabil ity of atlantoaxial reconstruction withanterior approach screw fixation through C2 vertebral body to C1 lateral mass and Gall ie’s technique (ASMG) for C1,2instabil ity. Methods Twenty-five human cadaveric specimens (C0-3 ) were divided randomly into 5 groups (n=5). Thethree-dimensional ranges of motion C1 relative to C2 were measured under the five different conditions：the intact state group (group A), type II odontoid fracture group (group B), posterior C1,2 transarticular screw fixation group (group C), ASM group (group D) and ASMG group (group E). The three-dimensional ranges of motions C1 relative to C2 by loading ± 1.5 Nm were measured under the six conditions of flexion/extension, left/right lateral bending, and left/right axial rotation. The obtained data was statistically analyzed. Results In each group, the three-dimensional ranges of motion C1 relative to C2 under the six conditions of flexion/extension, left/right lateral bending, and left/right axial rotation were as follows: in group A (8.10 ± 1.08), (8.49 ± 0.82), (4.79 ± 0.47), (4.93 ± 0.34), (28.20 ± 0.64), (29.30 ± 0.84)°; in group B (13.60 ± 1.25), (13.80 ± 0.77), (9.64 ± 0.53), (9.23 ± 0.41), (34.90 ± 0.93), (34.90 ± 1.30)°; in group C (1.62 ± 0.10), (1.90 ± 0.34), (1.25 ± 0.13), (1.37 ± 0.28), (0.97 ± 0.14), (1.01 ± 0.17)°; in group D (2.03 ± 0.26), (2.34 ± 0.49), (1.54 ± 0.22), (1.53 ± 0.30), (0.80 ± 0.35), (0.76 ± 0.30)°; in group E (0.35 ± 0.12), (0.56 ± 0.34), (0.44 ± 0.15), (0.55 ± 0.16), (0.43 ± 0.07), (0.29 ± 0.06)°. Under the six conditions, there were generally significant differences between group A and other four groups, and between group B and groups C, D and E (P lt; 0.001), and between group E and groups C, D in flexion/ extension and left/right lateral bending (P lt; 0.05). There was no significant difference between group E and groups C, D in left/right axial rotation (P gt; 0.05). Conclusion In vivo biomechanical studies show that ASMG operation has unique superiority in the reconstruction of the atlantoaxial stabil ity, especially in controll ing stabil ity of flexion/extension and left/right lateral bending, and thus it ensures successful fusion of the implanted bone. It is arel iable surgical choice for the treatment of the obsolete instabil ity or dislocation of C1, 2 joint.