Many variant configurations for Stirling engines have been presented. In Beta and Gamma type configurations, a displacer moves the working fluid between hot and cold sources. Whereas in the Alpha type there is no such a part and it has much simpler structure than the Beta and Gamma type. Therefore in this study, a novel configuration is introduced for Stirling engine the displacer is replaced by two pistons and cylinders. With this replacement, the new configuration can be called 3-Cylinders Gamma configuration for Stirling engine. Similar to Alpha type engine, this configuration has simpler structure and manufacturing process. For evaluation of new configuration, a simulation model of fabricated Gamma Stirling engine is prepared based on new configuration and geometry of ST-500 engine. The modeling is developed in GT-Suit software which is an industry-leading simulation tool. Maximum error between the experimental results and simulation of the new engine is about 20 percent for heat consumption and 14.7 percent for power. Thermodynamic analysis of performance parameters is done after the validation. The thermodynamic analysis results indicate that the increment of engine speed does not have appropriate effect on the performance and it led engine efficiency reduction. On the other hand by increasing the pressure and hot source temperature the engine performance improves and led higher thermal efficiency.