After decades of research, the problems and behavior of the corrosion of reactor alloy materials under service conditions are clearly understood. However, some problems in corrosion of reactor materials have not been clarified, including the critical corrosion process of the reactor materials under operational conditions, the role of a single factor in the corrosion process, and the prediction of corrosion behaviors of new materials in extreme environments. The density functional theory (DFT), which is based on quantum mechanics, can be employed to accurately predict the motion process of atoms and the change in the relevant energy within a very short period. The DFT has become an important auxiliary method for investigating the corrosion process of reactor alloy materials in recent years and can help solve the above problems. In this paper, the DFT is firstly introduced, which mainly includes the theoretical basis, development process, and mainstream computational software. Then, a comprehensive discussion and analysis are conducted on the current research status of DFT applied to the corrosion of reactor alloy materials, including the adsorption, separation, combination, and internal diffusion of the reactor alloy material surfaces in the environments of water-cooled reactor, liquid-metal-cooled reactor, and molten salt reactor. Finally, future development trends of DFT application in the corrosion of reactor alloy materials are prospected.