This study investigated the effect of the Cr/Al ratio on the microstructure and steam oxidation behavior of Fe-Cr-Al alloys at temperatures between 1000 ℃ and 1300 ℃. The results indicated a two-step oxidation process, including initial fast oxidation and film formation followed by long-term oxidation. The oxidizing film on the surface was dominated by submicron grain-sized Al₂O₃ and its thickness increased with the Cr or Al ratio. For the alloys with a high Cr or Al ratio, the rapid formation of a surface-oxidizing film acted as a passivation layer to reduce the water molecule diffusion rate, as confirmed by the corresponding exponential oxidation factor.