The influences of different In contents (3.0, 3.4, 3.8, 4.2 wt.%) on hardness and microstructure were investigated at different internal oxidation temperatures (650, 700, 750℃, respectively).The result shows that there is little change in hardness values when In content is ≤3.8% and the hardness decreases obviously as In content increases to 4.2%.The above phenomenon can be explained by the fact that oxide particle size varies little until In content raises to 4.2%, as a result of which the hardness reduces.Because the grain size rises gradually as internal oxidation temperature increases, the hardness decreases.The oxygen diffusion coefficient is small at low temperature and some solute elements (such as In and so on) diffuse into the oxidized zone, therefore oxide aggregation appears.The oxygen diffusion coefficient increases significantly and oxygen diffusion plays a major role in the alloy as the temperature rises to 750℃, thus little oxide aggregates.