Abstract: Under the global low-carbon energy transition, small nuclear reactors have emerged as a kind of crucial research object and development trend to overcome the limitations of large-scale nuclear power applications, which show the advantages such as lower investment costs, shorter construction cycles, and multi-scenario applicability. The research progress of various reactors worldwide was investigated in this paper, systematically examining the technical characteristics and industrial application prospects of light-water reactors, high-temperature gas-cooled reactors, liquid metal-cooled reactors, and molten salt reactors. Building on current domestic and international research, it summarized and elaborated on five key technologies for small nuclear reactors, i.e. advanced material development and component manufacturing, irradiation testing of structural materials and fuels, intelligent instrumentation and control systems, high-efficiency power conversion systems, and digital twin and intelligent operation-maintenance technologies. Furthermore, the study explores nuclear reactors’ application potential in the petrochemical industry, digital field, space exploration and deep-sea power supply fields, proposing that energy systems which integrate multi-scenario adaptability will give insights to the future trajectory of nuclear reactor development.