Degradable metals, represented by magnesium and magnesium alloys, have attracted significant attention as fracture internal fixation and bone defect repairing materials due to their good biocompatibility, suitable elastic modulus and degradable properties. The Mg-3Zn-1Ca-0.5Sr (wt%) alloy is considered a competitor in the biomaterial field thanks to its unique composition of essential nutrients and excellent mechanical properties. However, the presence of coarse second-phase particles in the alloy accelerates its degradation rate and causes excessive gas formation during implantation, which restricts the alloy's potential for clinical device applications. In order to further optimize the properties of the alloy, extrusion combined with high-pressure torsion (HPT) was adopted for deformation processing. The results show that 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, mechanical properties, and corrosion resistance of the alloy. After 15 cycles of HPT processing, the grains of the alloy are significantly refined to the nanometer scale, reaching approximately 98 nm. Additionally, the second-phase distribution is greatly improved, transforming the original streamlined structure into a more dispersed distribution. This change in microstructure leads to a significant strengthening effect on the alloy, with a noticeable increase in hardness from 60.3 HV in the as-extruded state to 98.5 HV.