In this study, we performed three surface modifications for AISI H13 steel to study their protective effects in 1023 K molten aluminum. Results showed that air oxidation can produce a thin film of Fe2O3 and little FeO, and the liquid-nitriding formed a surface of iron nitrides and oxides (Fe2O3 + Fe3O4). While liquid-nitriding with post-oxidation can form a surface of Fe3O4 and little Fe2O3 by oxidizing the nitrides into Fe3O4 on the liquid-nitriding samples. The Fe3O4 has low wettability and good chemical stability against molten aluminum, thus the corrosion behaviors of molten aluminum to the samples change from dissolution to oxidation.