Abstract: Tritium is one of the common radioisotopes in the nuclear power plant. In heavy water reactors, tritium causes the higher internal exposure because of the reactor design. Third Qinshan Nuclear Power Plant (TQNPP) is the only heavy-water-reactor nuclear power plant in China, which has 2 CANDU6 reactors. Since TQNPP were put into commercial operation in 2003, TQNPP strictly performs area and individual tritium radiation monitoring, continuously improves monitoring techniques and personnel protection methods for tritium internal exposure, ensuring the occupational safety and healthy of plant staffs. From 2003–2022, none of incident caused by tritium internal exposure which the effective dose is above the regulatory limits was occurred, the average individual annual tritium internal effective dose is lower than 200 μSv, and the percentage of the average annual tritium internal exposure collective dose is 18.6%, which is lower than the average level of 20%–30% around the global heavy water reactor plants, showing that the management practice of tritium internal exposure monitoring and protection in TQNPP is effective.