Objective To study the effect of stress on the degradation rate in vitro of new magnesium alloy bone screw. Methods A three-dimensional model of the tibia was established using a reverse engineering method, the stress distribution of the bone screws were calculated by finite element (FE) analysis. Then, based on the FE model, the in vitro degradation experimental device for bone screws in mechanical environment was designed, the stress distribution of the screw was used to load the in vitro experimental load, which effectively improved the accuracy and efficiency of the experiment. The experimental samples were divided into four groups, A, B, C, and D, Group A was treated as a control group with no additional force, while Groups B, C, and D were subjected to axial forces of 150, 250, and 350 N. In the experiments, H2 was collected, weight loss was measured, and the surface topography was observed to study the influence of the different mechanical environments on the degradation rate of the bone screws in vitro. Finally, combined the stress distribution with the degradation experiment results in vitro, the curve between stress and the degradation rate of new magnesium alloy bone screws in vitro was obtained. Results The results of FE analysis showed that the stress was mainly concentrated to parts II and IV, followed by part III, parts I and V were lower. Degradation experiments in vitro showed that the Group A had the lowest weight loss and hydrogen production, and the average degradation rate was (0.315±0.005) mm/a. While in the stress group, the weight loss and hydrogen production were increased gradually with the increase of axial force. The average degradation rates of Group B, C and D were (0.379±0.006) mm/a, (0.469±0.007) mm/a and (0.547±0.009) mm/a, respectively. The degradation rate increased with the increase of axial force. Conclusions When the new magnesium alloy bone screw was degraded in mechanical environment, the greater stress on the screw was, the faster the degradation rate in vitro was. The relationship between the maximum stress and the average degradation rate in vitro of the new magnesium alloy bone screws was obtained, which provided data support and theoretical guidance for material selection, design and clinical application of magnesium alloy bone screws.