Obejective Comparison of biomechanical stability of atlas pedicle screw (PS) and lateral mass screw (LMS) under osteoporosis by finite element method. Method According to the CT scan data of a normal male atlas, the three-dimensional model of atlas was reconstructed reversely, and then the osteoporosis model was established by setting the material properties of HyperMesh 12. Finally, abaqus6.9 was used to analyze the pull-out process of atlas PS and LMS under unicortical and bicortical insertion, and compare their stability. Results 1.In the osteoporosis model, the descending order of maximal pullout force was bicortical PS (878.886N) > unicortical PS (741.155N) > bicortical LMS (310.728N) > unicortical LMS (294.267N). 2.The stress of unicortical PS was distributed in the proximal and middle part of the screw body, and the stress near the entry point was the largest; the stress of bicortical PS was distributed in the whole screw, and the stress from the middle to the proximal end was greater, and the stress was greater when it was closer to the end. 3.The maximum stress of unicortical LMS was located at the screw thread of the screw entry point; the stress of bicortical LMS was distributed at the proximal and distal ends of the screw, among which the proximal stress was the biggest. Conclusion PS can provide sufficient stability for atlas fixation in patients with osteoporosis due to its long screw path, stress dispersion and strong "pedicle". Only by improving the screw design reasonably can LMS improve the effective mechanical stability.