Abstract: Free piston Stirling engine(FPSE)can use many kinds of heat sources,such as radioactive isotope heat source,nuclear energy and solar energy,etc.to convert thermal energy into mechanical energy.Due to high efficiency,high reliability and long life,it has become one of ideal potential machines to meet the current long-period deep space exploration missions.In this paper,the development process of FPSEs used in radioisotope power device and nuclear fission power system is presented in detail.It is concluded that the development process is mainly shown in the diversified structure of FPSEs,the expanding of output power and application scope,and the system integration.The key technologies of free piston Stirling engine are further summarized,and the theoretical research development of FPSEs in thermodynamics analysis,multi-objective optimization and dynamics are also shown.Finally,several thoughts are provided according to the development status of FPSE.