In this paper, a femtosecond green laser with wavelength of 515 nm was used to process the AZ31 magnesium alloy. The laser ablation threshold and ablation rate of Mg alloy were calculated. The mechanism of femtosecond green laser process was determined. The effects of surface microstructures on corrosion rate of AZ31 magnesium alloy was compared and analyzed. The results show that the laser ablation threshold of AZ31 magnesium alloy is 1.46 J/cm2, the ablation rate is 0.68 μm/pulse in the laser fluence of 8.36 J/cm2, the ablation rate increases with the laser fluence increasing. The high-quality holes can be fabricated with the laser fluence of 8.36 J/cm2 and the pulse number of 1000. In terms of the corrosion rate of magnesium alloy, the groove structure is less than that of the columnar structure and less than that of the smooth surface, among which the corrosion rate on the microstructural surface is about 1/3~1/2 of that on the smooth surface in 24 hours.