Abstract: Nuclear energy is a clean, efficient and high-quality modern energy. It is of great significance to alleviate energy shortage, improve ecological environment and optimize energy structure. As a kind of the fourth generation nuclear power system, high-temperature reactor has good inherent safety and economy, high power generation efficiency and wide application of process heat. The superior performance of high-temperature reactor is closely related to the excellent alloy materials. Due to the high temperature of helium in the primary circuit of high-temperature reactor, a trace of graphite dust generates certain gas impurities after chemical reaction. At the same time, due to the introduction of impure helium and gas leakage, the helium in the main coolant of high-temperature reactor contains trace gas impurities such as CO, H₂O, CH₄, CO₂, N₂ and O₂, and the concentration of impurities is in the order of ppm. Impurities in high-temperature environment will cause corrosion, oxidation, carburization and decarburization of alloy materials in high-temperature reactor steam generator and intermediate heat exchanger, and affect the reliability and safety of equipment. Inconel 617, Hastelloy X and Incoloy 800H are three candidate materials for high-temperature reactor intermediate heat exchanger and steam generator equipment. According to the studies, it shows that the chromium rich oxide layer formed on the surface of NiCr alloy at high temperature is an important factor to prevent serious corrosion of the alloy at high temperature. In this paper, the corrosion behavior of three alloys in high temperature helium containing ppm impurity was studied, and the effect of pre-oxidation in extremely low oxygen partial pressure He-1 atmosphere on the corrosion behavior of three alloys was explored. After the test, the corrosion results of the alloy with or without pre-oxidation were analyzed by weighing, scanning electron microscope, X-ray energy spectrum analysis, electron probe microanalyzer and carbon sulfur analyzer. The results show that the three alloys have different oxidation and carburization phenomena, and the carburization behavior has ended when they are corroded for 50 h. CH₄ plays an important role in the carburizing corrosion process of alloys. Pre-oxidation has no obvious improvement on the corrosion resistance of Hastelloy X alloy, less improvement on the oxidation resistance and carburizing capacity of Inconel 617 alloy and less improvement on the carburizing corrosion resistance of Incoloy 800H alloy. According to the test results, it can be concluded that the oxide layer formed by short-time pre-oxidation in extremely low oxygen partial pressure He-1 atmosphere is not necessary to improve the corrosion resistance of the alloy.