In this study, we first validated the oxidation performance of Alloy 800 (Fe-based alloy) and 625 (Ni-based alloy) within the temperature range of 700-1000 °C. After 24 hours of oxidation at 1000°C in air, the mass gain is measured as 2.53 and 1.86 mg/cm2 for Alloy 800 and 625, respectively, with their increase rates approximately reaching 6 times compared with those at 900 °C. The main oxidation scale in both two alloys is identified as a Cr2O3 layer with minor NiCr2O4 from 800-1000 °C. A crucial facet of this investigation involved subjecting the alloys to pre-oxidation treatment at 1000 °C for 24 hours, resulting in reduced mass gain during subsequent hot corrosion evaluations with NaCl/Na2SO4 salts at 900°C, particularly noticeable in Alloy 800, where a dense oxidation layer formed. However, cross-sections of both two alloys show a deep penetration by Na and O. These findings reveal the limited protective role of the Cr2O3 layer in augmenting resistance to hot corrosion while offering valuable insights into materials' performance in high-temperature environments and industrial applications.