Abstract: As a significant space energy technology, space reactor technology possesses unique advantages and demonstrates broad application prospects in the space domain. The classification system of space nuclear energy was outlined, and the characteristics and basic performances of various space power supplies and space propulsion technologies were introduced. The performance advantages of space reactor power supplies over other power sources were analyzed. An overview of the development history of The United States and Russia in the fields of space nuclear power systems and nuclear thermal propulsion was presented. The characteristics and applicable scopes of various space nuclear power and nuclear thermal propulsion technical solutions were summarized. Through specific case studies, their technical schemes and key technical parameters were analyzed and introduced. Key technologies involved in space reactor technology were analyzed in detail, including high-temperature compact reactor design, high-efficiency thermal-electric conversion, radiation protection optimization, etc. The development trends of space reactor technology were analyzed and summarized, and its application requirements and prospects in fields such as Earth-orbiting space, Lunar research stations, Mars exploration, Jupiter system exploration, deep space exploration, and hazardous celestial body defense were prospected. Space reactor technology plays an irreplaceable role in meeting future space mission demands, and its continuous development will have profound impacts on humanity’s exploitation of space resources and exploration of the vast universe.