Abstract: During the power operation of pressurized-water reactor (PWR) nuclear power plants (NPPs), ⁴⁰Ar in air of the reactor cavity will be activated by neutron, and becomes the radioactive nuclide ⁴¹Ar. In this paper, two dimensional discrete ordinates transport calculation code DORT was used to analyze the neutron fluence rate in reactor cavity, and evaluated nuclear data processing system NJOY code was used to process ENDF/B-Ⅶ.0. The ⁴⁰Ar neutron capture cross section was generated by NJOY code which used the flux generated by DORT as the weight function. The generation rate and environment release source term of ⁴¹Ar by ⁴⁰Ar neutron capture reaction in the reactor cavity in million kilowatt PWR NPPs were analyzed. The analysis method in the paper can be used to determine the optimum estimation value of ⁴¹Ar source term in the design of PWR NPPs.