Abstract: Tritium research including tritium generation in reactor core and in the primary coolant, release pathways, tritium chemical forms and release amount is a very important part of environment assessment of nuclear power plant. Based on the international operation practice, the primary coolant system, auxiliary systems, radwaste system and ventilation system were analysed, and the tritium release pathways and chemical forms were investigated. The results indicate that the theoretic calculation results agree with the nuclear power plant operation data very well. The tritium contained in the primary coolant is mainly produced from the three-fragment fission reaction, boron activation in the burnable poison rods and boron, lithium and deuterium activation when they pass through the core. The released tritium to the environment is mainly in the form of tritiated water and the percentage between the liquid and gaseous of release tritium mainly depends on the leakage rate from the primary coolant to the reactor building and auxiliary building.