Abstract：As a new and advanced reactor system of nuclear power plants, the high temperature gas-cooled reactor has received more and more attention for its advantages in enhanced safety and highly economical and modular structure. In China, the first model power plant of the High Temperature Gas-cooled reactor (HTR-PM) is started its construction at Shidao Bay, Rongcheng, Shandong Province. This paper presents calculations of the total radioactivity inventory of HTR-PM core and the analysis of the environmental impact of the plant, using KORIGEN code. Some segments of the code were recompiled to consider the change of spectral indices in input data which reflects the realistic neutron situation in the reactor core. The half-life data of isotopes are updated and corrected. A reasonable flow-line model is built. Finally, the total inventory of radioactivity in HTR-PM reactor core is obtained, which approaches the actual one to provide a basis for safety analysis and management of HTR-PM, and for accounting of nuclear elements.