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In order to ameliorate the microstructure characteristics and degradation behavior of the medical Mg alloys, the extrusion process was conducted to change the grain size characteristics and the distribution law of secondary precipitates/intermetallic compounds, and the microstructure characteristics and degradation behavior of as-extruded Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy were analyzed. Results show that different hot-extrusion deformation methods do not change the types of the secondary phases in Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy, but change their distribution and morphology. The main components of Mg-2Zn-0.5Gd-1Y-0.5Mn Mg alloy are α-Mg and W-Mg₃Y₂Zn₃ phases. The electrochemical tests demonstrate that the corrosion current densities are 2.498, 3.656, and 1.012 μA·cm^-2 for as-cast, extruded/370 °C, and extruded/390 °C Mg alloys, respectively. The precipitates/intermetallic com-pounds of strip shape are distributed in the matrix of as-cast Mg alloy, which can act as the micro-cathode, thus forming the galvanic-corrosion sites and accelerating the corrosion rates. Partial coarse precipitates cannot completely dissolve into the α-Mg matrix due to the low actual temperature of the Mg alloy during extrusion at 370 °C. With the disordered distribution and the increasing precipitates, the area proportion of micro-cathode is increased, which accelerates the corrosion rate. However, for the Mg alloy during extrusion at 390 °C, the extrusion speed is fast, the dissipation behavior is slow, and the friction between ingot and extruder is intense, indicating the occurrence of sufficient dynamic recrystallization, which reduces the number/area of micro-cathode and improves the corrosion resistance.