In recent years, degradable metals, represented by magnesium and magnesium alloys, have gradually become the research focus of fracture internal fixation and bone defect repair materials due to their good biocompatibility, suitable elastic modulus and degradable properties. The Mg-3 wt%Zn-1 wt%Ca-0.5 wt%Sr alloy is considered a competitor in the biomaterial field thanks to its unique composition of essential nutrients and excellent mechanical properties. However, due to the existence of coarse second phase in the alloy, the degradation rate of the alloy is too fast, and there is a serious phenomenon of gas production during implantation, which limits the clinical promotion and application of the alloy. In order to further optimize the properties of the alloy, this study adopts extrusion composite high pressure torsion (HPT) for deformation processing. By optimizing the material processing means, the grain can be refined and broken, and the second phase distribution can be improved, thus improving the microstructure of the alloy, and then improving the mechanical and corrosion resistance of the alloy. The high pressure torsion deformation process is applied to the processing of magnesium and magnesium alloys. It can improve its potential in biomedical applications. The results showed that after HPT processing, the grains at the periphery of the alloy were significantly refined to a nanometer level, reaching approximately 98 nm, the distribution of the secondary phase also improved significantly, transforming the original streamlined organization into a dispersed distribution. This change in microstructure led to a significant strengthening of the alloy, with a noticeable increase in hardness from 60.3HV in the as-extruded state to 98.5HV.