Abstract: During AP1000 operation, the water itself in the primary loop and special nuclides added in the water will be activated by neutrons. Tritium is main activation product and it is drawing more and more attention as they are almost discharged into environment in form of gas or liquid. Therefore, it’s essential to study tritium generation in the primary coolant. In this paper, the tritium generation and consumption mechanism of the primary coolant in AP1000 nuclear power plant was studied and the tritium calculation model was established. Based on the tritium calculation model, the tritium activity in the coolant loop of AP1000 was calculated and the contribution of various ways to generate tritium was analyzed. The results show that the quantity of tritium is mainly from the activation reaction of soluble boron by absorbing neutron and fission of uranium, which contributes more than 80%. The tritium production in AP1000 primary coolant is 5.23×10¹³ Bq/a at the purity of ⁷Li is 99.9%, which accounts for 14.01% of total tritium production. With the increase of ⁷Li purity, the contribution of lithium decreases linearly. When the purity of ⁷Li is 99.99%, the tritium produced from lithium accounts for 3.18%. Based on the above results, the generation of tritium in coolant can be reduced by controlling the initial boron concentration added in coolant, improving the quality of the fuel cladding, and increasing the purity of ⁷Li in LiOH.