The high temperature gas-cooled reactor pebbled-bed module (HTR-PM) which is a modular high temperature gas-cooled reactor demonstration power plant, is characterized by inherent safety features and high generating efficiency. It adopts numerous graphite for structural materials in the reactor core, helium as primary coolant, and tristructural isotropic (TRISO) coated particles embedded in the graphite matrix as fuel elements. However, at high temperature the impurities in the helium can react with the graphite to cause corrosion of structural materials. Therefore, it is very necessary to monitor and control the composition and content of gaseous impurities in the primary coolant. In HTR-PM, the gas sampling and analyzing system has been designed to sample the primary helium at different positions in the helium purification system which is used to reduce the quantity of chemical impurities and remove the radioactive dust and gaseous fission products in the primary loop, and monitor the gas composition and individual concentration online. In the current paper, the composition of the gaseous impurities which need to be monitored in the primary loop of HTR-PM is presented, the design of the gas sampling positions in the helium purification system is discussed, and the main gas analyzing instruments are introduced.