Abstract:AZ31 magnesium alloy surface was carried out solid diffusion Zn+La2O3(the mass fraction of La2O3 in the diffusion agent was 0.4%) treatmentat 390 °C, the diffusion time was 0,2, 4 and 6h respectively.The changes of the surface microstructure of magnesium alloy at different times of diffusion were studied. The surface hardness and corrosion resistance of the magnesium alloy were tested. The results show that no diffusion layer appeared when the diffusion time was 2 h. solid solution Mg0.97Zn0.03 andMg-Zn compounds(MgZn+Mg2Zn3+MgZn2+ Mg2Zn11) appeared on the diffusion layer when the diffusion time was 4 h. With the prolonged diffusion time, Zn atom diffusion ability was enhanced and variouscompoundswere formed by Mg and Zn reaction. The diffusion layer was obtained on AZ31 magnesium alloy surface.When the expansion time was 6 h, Mg7Zn3 as a new phase was present in diffusion layer, the microstructure of diffusion layer became coarse at the same time. The hardness increaseedwith the increase of the diffusion time, and the corrosion resistance was optimal when the diffusion time was 4 h.