Abstract: Space power is one of the core technologies for space exploration. Space nuclear reactor power is characterized by high energy density, wide power coverage and small dependence on space environment, which is a promising choice for future space power. In this paper, the existing space power systems in view of mission targets and system specific mass were compared, potential application of space nuclear reactor power in future space activities was presented. Based on the investigation of the future civil and military space missions, the power requirement of space nuclear reactor power was summarized. According to different powers, the various technology schemes for space nuclear reactor power in the open literatures were compared, and the relatively optimized technical roadmaps for different power levels were given. This study can provide guidance for the space nuclear reactor power system design.