Abstract: Although the degradability and biosafety of magnesium alloys make them advantageous for biological applications, medical implants made of magnesium alloys often fail prematurely due to corrosion. Therefore, improving the corrosion resistance of magnesium alloys has become an urgent problem in the alloy design process. In this study, we designed and prepared Mg–xZn–0.5Y–0.5Zr (x = 1, 2, and 3, wt%) alloys in a hot extruded state and analyzed their surface structure through scanning electron microscopy, energy dispersion spectrometry, and X-ray diffraction. It was found that increasing the Zn content refined the recrystallized grains in the alloy. Particularly in Mg–3Zn–0.5Y–0.5Zr, the I phase became finer, forming both granular and nanoscale needle-like particles. Surface characterization after the immersion experiment showed that the corrosion product layer was mainly composed of Mg(OH)₂, Zn(OH)₂, CaCO₃, and hydroxyapatite. The degradation rate of ZW305K was the lowest, measured as 4.1 and 6.0 mm/a with the hydrogen precipitation method and weight loss method respectively. Electrochemical experiments further explained the corrosion circuit model of the alloy in solution and confirmed the earlier results. The maximum polarization resistance of ZW305K was 874.5 Ω·cm², and the lowest corrosion current density was 0.104 mA/cm². As a biomedical alloy, it must exhibit good biocompatibility, so the alloy was also tested through cytotoxicity, cell adhesion, and staining experiments. The cell viability of each group after 48 h was greater than 80%, showing that the addition of zinc enhances the alloy’s biocompatibility. In summary, the prepared alloys have the potential to be used as biodegradable implant materials.