Regenerator is the main component in improving the efficiency of the Stirling engine to approach the ideal efficiency. Optimization of Geometry and materials of regenerator, amount and quality of porosity of regenerator is studied in this research. The main idea of this study was to evaluate the effect of porosity, and porosity gradient in pressure lost and the axisymmetric thermodynamic regeneration. In order to comprehensive analysis, the three models of regenerator are simulated. In model one, porosity is constant in the length of regenerator (common model). In model two, the regenerator porosity is changed from high to low in the length of regenerator. In the model three, the regenerator porosity is changed from low to high in the length of regenerator. All versions of model have the same net porosity. Each of these models separately are simulated in Ansys software and validated with experimental results from a laboratory sample. The results show that in the second model with a small increase in pressure drop during recovery, the amount of energy recovery increase dramatically compared to the conventional model.