The power system of a free piston Stirling generator (FPSG) based on potassium heat pipes has been developed in this paper. Thanks to the advantages of long life, high reliability, and high overall thermal efficiency, the FPSG is a promising candidate for nuclear energy, especially in space exploration. In this paper, the recent progress of FPSG based on nuclear reactor for space use was briefly reviewed. A novel FPSG weighted only 4.2 kg was designed, and one dimensional thermodynamic modeling of the FPSG using Sage software was performed to estimate its performance. The experiment results indicated that this FPSG could provide 142.4 W at a thermal-to-electric efficiency of nearly 17.4%. Besides, the power system integrated with four FPSGs and potassium heat pipes was performed and the single machine failure test was conducted. The results show that this system could provide an electrical power of 300 W at an overall thermal efficiency of 7.3%. Thus, it is concluded that this power system is feasible and will have a great prospect for future applications.