Abstract: To establish a lunar base, the problem of energy supply needs to be solved first. The nuclear reactor power system has the advantages of high power, long service life and environmental resistance ability. It is an ideal energy solution option for lunar base and other deep space exploration missions. The brief analysis of the current status of energy that can be used for the lunar base was carried out. The design idea of 40 kWe nuclear reactor power system for lunar base was proposed. After the preliminary optimization design, process and overall design parameters of the system were given. Finally, the system scheme was analyzed and demonstrated from the aspects of reactor physics, shielding, thermodynamics and structure. The results show that the system scheme is reasonable and feasible. It can meet the requirements of safety and lifetime.