Abstract: SiC_f/SiC composites were successfully developed in the 1980s and have shown significant potential in the nuclear energy field due to their excellent properties, such as resistance to neutron irradiation and high-temperature tolerance. This paper systematically reviews the research progress of SiC_f/SiC composites in nuclear energy applications over the past 50 years. In terms of fusion reactor applications, the design schemes and key operational parameters of SiC_f/SiC composites in the U.S. ARISE fusion reactor, the Japanese DREAM fusion reactor, and the French TAURO fusion reactor are summarized. For fission reactor applications, the design and application plans of SiC_f/SiC composites in various reactor types, such as gas-cooled reactors and molten salt reactors, are introduced, including the U.S. EM² gas-cooled reactor, the French ALLEGRO gas-cooled reactor, and the U.S. Sm-AHTR molten salt reactor, along with their key operational parameters. Additionally, the development plans for SiC_f/SiC composite cladding under the U.S. Department of Energy's Accident-Tolerant Fuel program and the current technological status of SiC_f/SiC composite cladding development in the U.S., France, and China are highlighted. Although SiC_f/SiC composites are considered important candidate materials for the blanket of tokamak fusion reactors and the cladding of fission reactors, challenges such as reduced thermal conductivity after irradiation, high-temperature water-oxygen corrosion, and post-irradiation cracking remain significant technical bottlenecks limiting their engineering applications. It is recommended to make targeted adjustments in fiber weaving structures, fiber volume fraction, fiber interface characteristics, and composite densification processes to address the challenges faced by SiC_f/SiC composites in practical engineering applications within reactors.