Abstract: Intermediate heat exchanger is the key component of indirect high-temperature gas-cooled reactor (HTR) helium turbine cycle and high-temperature process heat applications. Intermediate heat exchanger belongings to the first loop pressure boundary, and it transfers the helium heat of temperature of 900-1 000 ℃ at core exit to the second loop helium, in addition it also endures helium pressure between two loops. So far the heat-resistant metallic materials used in the intermediate heat exchanger are very limited. There are H₂, H₂O, CO, CH₄ and other impurities in first and second helium loops of HTR, the impacts of high temperature helium impurities to the intermediate heat exchanger material are mainly oxidation, carbonization and decarbonization, reducing material’s mechanical properties, and its impact can not be ignored. To design intermediate heat exchanger, temperature range of the existing standards needs to be extended, and the impact of helium impurities on the strength of material must be considered.