Abstract: The supercritical carbon dioxide (S-CO₂) nuclear energy and power system uses S-CO₂ as the working fluid to convert nuclear heat directly or indirectly into electricity or mechanical energy. S-CO₂ is considered one of the most promising working fluids for applications in conventional and high-temperature scenarios. The unique properties of S-CO₂, such as its non-phase-change behavior, high density, compressibility near the pseudo-critical region, low thermal cycle compression ratio, minimal thermal inertia equipment requirements, and suitability for direct cycle and power generation propulsion technologies, simplify the system, reduce volume, lower weight, improve maneuverability, reduce noise, and enhance thermal efficiency. The advantages of S-CO₂ power conversion technology not only meet the development needs of the next generation of advanced energy conversion technology but also align with the future trends of nuclear power systems. Leading energy technology countries, including the United States, conducted extensive research on S-CO₂ power conversion technology in areas such as fossil fuel power generation, nuclear energy, waste heat recovery, and solar thermal power. Some of these projects have already entered the engineering demonstration phase. In China, S-CO₂ power conversion technology was included in the “14th Five-Year Plan” for scientific and technological innovation in the energy sector. Numerous universities and industrial sectors in China are actively conducting research and development in this field. The development of S-CO₂ nuclear power system in three historical stages for nearly 60 years, including the concept creation, research restart, and collaborative innovation, was summarized in this paper. The research status of S-CO₂ nuclear energy and power system in reactor design, material technology, thermohydraulics, heat exchangers, turbomachines, system operation, control, and security policies was also introduced. The technical challenges and key research directions faced by S-CO₂ nuclear energy and power system in basic research and engineering were pointed out. Currently, energy superpowers represented by China and the United States have completed laboratory tests of S-CO₂ power conversion systems, and are expected to move towards medium-scale engineering demonstration or even large-scale application in the next 5 to 10 years. S-CO₂ nuclear energy and power system has the prerequisites for engineering development, and is expected to lead the transformation of advanced nuclear energy technologies. Nevertheless, numerous technical challenges are still existing in core design, materials, thermal-fluid mechanics, and safety analysis. Additionally, engineering efforts are required to tackle challenges related to high-efficiency heat exchangers, highpower high-speed electric motors, heavy-duty electromagnetic bearings, and turbine power generation systems. Simultaneously, coordinated efforts in both fundamental and applied research are essential to enhance the advanced nature and engineering feasibility of S-CO₂ nuclear energy and power systems.