Abstract: Aiming at the new requirements of the current development of space technology, based on the designs of the space nuclear power system proposed by foreign countries, a new concept of the nuclear power system design with a megawatt class space heat pipe reactor was designed. The core was a metal lithium heat pipe cooling, graphite moderated thermal reactor, and used drums to control reactivity. The core fission heat was rejected through the heat pipe. Different from the staggered arrangement of the fuel rod and the heat pipe in the foreign designs, a heat pipe-fuel composite element that the fuel was wrapped in the outer wall of the heat pipe was applied in this paper. The Brayton dynamic thermoelectric conversion using helium-xenon mixed gas as working fluid was applied as the energy conversion method. System waste heat was transferred by the sodium-potassium alloy cooling circuit to the potassium heat pipe radiation panels, and rejected into space by radiation. Physical and thermal analysis of the heat pipe reactor core and the performance analysis of heat pipe radiation panels were operated. The results show that the designed heat pipe reactor core meets the safety requirements under design power, and the heat pipe radiation panels have sufficient capacity to export system waste heat.