Abstract: Space nuclear reactor is the research foundation of space nuclear power and nuclear propulsion. The volume and mass of high-power nuclear reactor are always the important factors limiting the aerospace design. In view of this problem, the heat pipe radiation radiator of MW space nuclear reactor system was modeled and analyzed, and the thermal resistance model of the heat pipe radiation radiator was established in this study. The effect of the length L_f and thickness δ_f of the bare carbon fiber fin, the mass flow m of the coolant, the inlet temperature T_f1 of the radiation radiator on the mass M of the radiation radiator was discussed under the given conditions by the exhaustive method and genetic algorithm. The results show that when T_f1 is 800 K, L_f is 5 cm, δ_f is 0.16 mm, and m is 9 kg/s, M is the best. At this time, M is 906.593 kg, and 0.63% of the system mass is optimized.