Abstract: As a key material of nuclear power plant, the safe service of reactor cavity concrete is one of the prerequisites for the long-term stable and safe operation of nuclear power plant. In order to study the neutron irradiation damage mechanism of the reactor cavity concrete, obtain the test data of the reactor cavity concrete in the neutron irradiation environment, and provide a scientific basis for the long-term stable operation of the nuclear power unit, the irradiation test method of the reactor cavity concrete was established, and the irradiation test device with a water-passing basket structure was developed in this paper. The physical and thermal design of the irradiation test of the reactor cavity concrete was carried out with the numerical calculation method. The accelerated neutron irradiation test of the reactor cavity concrete was carried out in the 5# hole with a pressure tube in Minjiang Test Reactor (MJTR) by using the irradiation pile method with the reactor. The standard concrete samples of \phi 50 mm×50 mm and the small concrete samples of \phi 25 mm×25 mm were loaded in the cavity of the irradiation test section for the irradiation test device, and seven layers were arranged axially in the 1 000 mm active area of the reactor. During the irradiation test, the pressure tube was filled with the deionized water, and the concrete sample was directly in contact with the deionized water. The neutron flux and the irradiation test temperature were measured by the neutron detector and the thermocouple respectively. The irradiation test results show that the irradiation test method is feasible, the irradiation test device is reasonable, and the neutron irradiation of multiple concrete standard samples and small samples is realized. The cumulative fast neutron flux of the concrete sample (E≥0.1 MeV) is distributed in 2.38×10¹⁸-2.06×10¹⁸ cm⁻², the temperature of the irradiation test is stable during 50-60 ℃, and the irradiation test index meets the test requirements. Furthermore, the appearance inspection, size measurement and ballast test of the standard and small concrete samples before and after irradiation were carried out. The results show that compared with before irradiation, there is no obvious difference in the external shape of concrete samples, but the color of concrete samples changes greatly, the overall color of concrete samples is yellow-gray after irradiation, and the outer size of concrete samples has a certain increase. Therefore, under the irradiation condition of average fast neutron flux of 3.41×10¹⁸ cm⁻², there are certain irradiation swelling and mechanical performance degradation phenomenon of the reactor cavity concrete.