Magnesium alloy has many excellent properties such as low density, high specific strength and specific stiffness, good mechanical processing performance, and good biocompatibility. Magnesium alloy has become a potential new generation of biodegradable bone plate materials, but its poor corrosion resistance limits its development. In this paper, the effect of laser shock peening (LSP) on the corrosion resistance of AZ31B magnesium alloy was studied by using different laser power densities of 1.35 GW/cm2, 2.99 GW/cm2, 3.92 GW/cm2, the polarization curves were obtained by electrochemical measurement technique of dynamic potential scanning in 3.5% (mass fraction) NaCl solution for comparison of corrosion resistance before and after laser shock. The influence mechanism of laser shock peening on the corrosion resistance of AZ31B magnesium alloy was studied by microstructure. The surface hardness of the sample increases with the increase of laser power density. The surface hardness of the 2.99 GW/cm2 sample is 81.2 HV, which is 35.8% higher than that of the original sample. XRD patterns show that compared with the original sample, the diffraction peak of the sample after laser shock treatment shifts to the high angle direction, the intensity of the diffraction peak decreases, and the FWHM increases. The 2.99 GW/cm2 sample has the best corrosion resistance, corrosion potential is-0.602 41 V, corrosion current density is 1.021 5 × 10-4 A / cm2, corrosion potential increased by 50.47% compared with the original sample, and corrosion current density decreased by 42.90%.