Vuilleumier heat pump (VHP) is a heat driven heat pump that can be used for both heating and cooling. A free-piston Vuilleumier heat pump (FVHP) is described as an alternative approach to reduce the construction cost. In this paper, a thermodynamic model based on fundamental and empirical correlations is built to estimate the heat output and coefficient of performance (COP) of the FVHP under different configurations and operating conditions. Several prototypes are also designed and tested recently to verify the modeling results. Since parameters like heat exchanger length, regenerator thickness, chamber diameter and so on would affect the heat output and COP significantly, a multi-objective optimization is essential for the future FVHP design to achieve higher heat output and COP. The second version of Non-dominated Sorting Genetic Algorithm (NSGA-II) is integrated into the thermodynamic model for the multi-objective optimization. Necessary design parameters are considered as the decision variables. The heating output and COP of the FVHP are decided as the objective functions. A final optimal solution has been selected based on necessary decision-making approaches.