Abstract: In order to find out design methods of the free piston Stirling engine， Sage software is used to establish a one-dimensional model of the free piston Stirling engine（Re-1000）. The simulation results are compared with the experimental results. The simulation results showed the same changing trend with the experimental results in the values of the output power and thermal efficiency. The error of output power between the simulation value and the experimental value is about 15%. The simulation value of thermal efficiency is 4% larger than the experimental value. It is proved that the Sage software can simulate the free-piston Stirling engine with good accuracy. And this effort has certain significance on optimizing the performance of the free-piston Stirling engine.