The Ag-Mg alloy containing 0.2% Mg was prepared in vacuum induction melting and cold-machined into tube. The internal oxidation of the alloy was carried out in the atmosphere. The microstructure characteristics of different oxidation temperature and time were studied. The results show that the microstructure of Ag-Mg alloy is fine equiaxed grains after treatment at 500 ℃. When the temperature is higher than the 700 ℃, a fine-grained zone is formed on the surface. The inner grains grow up significantly, and the oxidation interface moves to the center. When the internal oxidation temperature is less than 600 ℃, the grain size of the Ag-Mg alloy grows linearly and the trend is relatively flat. When the temperature is above 600 ℃, the grains grow up rapidly. As the temperature increases, the depth of internal oxidation increases in a lower parabola. At 800 ℃, with the increase of oxidation time, the fine crystal region and internal grains is not change significantly, and the internal oxidation depth increases in a parabola.