The effect of hot extrusion with different extrusion temperatures (340, 360, 380, and 400 °C) on the microstructure evolution and properties of the as-cast Mg-1Zn-0.3Zr-1Y-2Sn magnesium alloy was investigated by optical microscopy (OM), scanning electron microscopy (SEM), immersion experiments, electrochemical experiment, and tensile test. The results show that after hot extrusion, the second phase of the alloy is broken into particles along the extrusion direction, while the grain size is significantly reduced, and dynamic recrystallization and deformation grains exist in the microstructure. As the extrusion temperature increases, the content of the second phase changes less, and the size of the dynamic recrystallization grain gradually increases. The mechanical properties of the extruded alloys are improved, but their corrosion resistance is weakened. The hot extrusion treatment can improve the corrosion resistance of the alloy in the early stage of corrosion, while as the corrosion proceeds, the corrosion resistance of the alloy in the later stage is weakened. When the hot extrusion temperature is 360 °C, the extruded alloy has relatively good mechanical properties and corrosion resistance.