The high-temperature gas-cooled reactor of Huaneng Shidao Bay Nuclear Power Plant in Shandong Province, as the world’s first nuclear power plant with the application of the fourth-generation nuclear power technology, uses helium as the coolant in the primary circuit. To ensure the purity of the helium in the primary circuit, a helium purification system is installed to remove various gaseous chemical impurities such as H2, CO, H2O, CO2, CH4, N2, O2 and radioactive impurities in the helium. The helium purification system is equipped with a copper oxide bed for oxidizing H2 and CH4 in the helium into H2O and a molecular sieve bed for adsorbing H2O in the helium to ensure the optimal purification efficiency. After the helium purification system works continuously for 1800 h, the purification equipment will approach the saturation state of operation. Close attention should be paid to the analysis results of impurities in the helium, and the purification train should be put into the regeneration process. To verify the composition of impurity gases in the helium of the primary circuit of the high-temperature gas-cooled reactor and further improve the operation efficiency of the helium purification system, this paper conducts an analysis of the activity concentration of H-3 in the helium of the primary circuit. The helium at the inlet and outlet of the helium purification system is sampled by a tritium sampling device, and measured by a low-background liquid scintillation counter to obtain data such as the activity concentration of different forms of H-3 and the purification efficiency of the helium purification system, providing data support for the optimal control of the operation of the helium purification system in the demonstration project, as well as theoretical support and practical guidance for the commissioning, overhaul and operation of subsequent projects.