Abstract: Aiming at operating characteristics of free piston Stirling engine and coupling relationship of inherent parameters,a full-time domain numerical model was established according to physical circumstance of pistons and working space. Thermodynamic parameters could be solved comprehensively through the model. Operating characteristics of LIP's 1 kW FPSE were obtained at different condition. Numerical results and experimental results were compared and conformity was realized. The numerical model is supposed to offer performance predictions and design guidance for further Stirling engines.