[en] The Cr-Ni-Mo-V heat-resistant low-alloy steel is used for VVER reactor pressure vessel material. The neutron irradiation of the reactor will cause the irradiation embrittlement of the RPV material, cause the change of the microstructure of the material, reduce its mechanical characteristics, affect the operating life of the RPV and the safety of the reactor. The irradiation embrittlement mechanism of RPV material is divided into reinforce mechanism and non-reinforce mechanism. Under the neutron irradiation, radiation defects are formed inside the material, and elements such as copper, nickel, manganese and silicon form irradiation-induced clusters, leading to material strengthening and hardening, phosphorus and other impurity elements segregate to the dislocation line, grain boundary or phase boundary, resulting in reduced grain boundary and phase boundary strength. There are synergistic effects of radiation embrittlement between nickel and manganese, nickel and copper, copper and phosphorus. (author)