The influences of the hot extrusion process on the microstructure, corrosion behavior and corrosion mechanism for Mg-Y magnesium alloy were studied by means of the microstructure observation, weight loss test, electrochemical test and corrosion morphology test. The results showed that with increasing of the extrusion ratio, the shear flow line on the vertical section of the extruded alloy increased, the shear bands parallel lines became more clearly visible, and a large number of fine equiaxed grains distributed in parallel with the flow lines. The open circuit potential had a certain degree of improvement after extrusion, the open circuit potential increased with increment of extrusion ratio, and the corrosion potential of the vertical section was higher than that of the same alloy in the same compression ratio. The shift rate of the corrosion potential relatively became larger with increasing of the extrusion ratio, and the cathode corrosion current corresponding to the branch migration shifted to the positive direction. The high frequency capacitive arc increased with increment of the extrusion ratio, and the radius of capacitive arc of the vertical section was slightly larger than that of the transverse section. The corrosion morphologies of Mg-0.25 Y alloy were uniform corrosion, and the corrosion morphologies of Mg-(2.5, 5, 8 and 15) were the pitting corrosion and the small range, deep depth localized corrosion. The influences of the hot extrusion process on the microstructure, corrosion behavior and corrosion mechanism for Mg-Y magnesium alloys were studied by means of the microstructure observation, weight loss test, electrochemical test and corrosion morphology test. The results showed that with increasing of the extrusion ratio, the shear flow line on the vertical section of the extruded alloy increased, the shear line parallel lines became more clearly visible, and a large number of fine equiaxed grains distributed in parallel with the flow lines. The open circuit potential had certain degree of improvement after extrusion, the open circuit potential increased with increment of extrusion ratio, and the corrosion potential of the vertical section was higher than that of the same alloy in the same compression ratio. increasing of the extrusion ratio, and the cathode corrosion current corresponding to the branch migrat ion shifted to the positive direction. The high frequency capacitive arc increased with increment of the extrusion ratio, and the radius of capacitive arc of the vertical section was slightly larger than that of the transverse section. The corrosion of morphologies of Mg-0.25 Y alloy were uniform corrosion, and the corrosion morphologies of Mg- (2.5, 5, 8 and 15) were the pitting corrosion and the small range, deep depth localized corrosion.