Abstract: Reactor shielding layer is usually made of reinforced concrete, which is of great volume and weight, and is one of the important parts of reactor decommissioning source term. The neutron flux rate and activation source terms in different positions of the shielding layer of the Heavy Water Research Reactor (HWRR) were calculated by using MCNP and ORIGEN programs with establishing the reactor 3D model. In order to verify the accuracy of the calculation model and the calculation results, a sample was obtained in the central area of the shielding layer of the HWRR, and the activity of ⁶⁰Co and ¹⁵²Eu in the samples was measured. The measurement results are in good agreement with the calculation results, which prove the accuracy of the theoretical calculation model. The activation depth of the shielding layer was calculated, and the results prove that the maximum activation depth of the shielding layer is about 600 mm. According to the calculation, it is proved that the decommissioning scheme of retaining the outer partial layer is theoretically feasible.