The trace number of impurities such as CO, H2, H2O, and CH4, which existed in the primary coolant of High Temperature Gas-Cooled Reactor (HTGR), has an adverse effect on the structural metallic materials at elevated temperatures. Mainly, it includes oxidation, decarburization, and carburization. The simulative corrosion test was conducted on the four alternative materials of the steam generator in HTGR: Inconel 617, Incoloy 800H, Hastelloy X, and T-22. At 950°C, the alloys were exposed to the helium and argon with impurities for 50 hours. The corroded samples were analyzed by weighing, scanning electron microscope (SEM), and electron probe microanalyzer (EPMA). Inconel 617, Incoloy 800H, and Hastelloy X formed the chromerich scale on the surface. Due to the low oxidizable elements content and low oxygen partial pressure, the continuous scale of T-22 alloy was not observed. Although Inconel 617 and Incoloy 800H formed the thick oxidation layer, pores on the surface may weaken the corrosion resistance. For Inconel 617, the Chromium Depletion occurred near the corrosion layer. In addition, the high temperature alloys showed similar corrosion behaviors in the helium and argon with trace impurities. This proves that the corrosion behavior of superalloys at 950°C will not change after replacing helium with argon, providing an alternative to helium in the corrosion test atmosphere.