In the current study, a comprehensive thermodynamic analysis (energy and energy analyses) of a beta-type Stirling engine has been performed at different working conditions. First, a non-ideal adiabatic model has been proposed for performance analysis of the Stirling engine and in order to increasing its accuracy, the frictional and thermal losses of Stirling engine have been considered. Also, for model validation, the operational and geometrical specifications of a beta-type Stirling engine which made in General Motors Corporation called GPU3 have been used. The results of the present model have been compared with the experimental data of NASA Lewis Research Center and the results of other previous adiabatic models. Then, the effects of engine rotational speed, mean engine operating pressure, and regenerator length on energy efficiencies and energy destruction have been investigated for two working gases of helium and hydrogen. The results show that with increasing the engine rotational speed, the frictional and thermal losses increase, and the energy efficiency reaches to its maximum value at shorter lengths of regenerator. Also, with increase of the mean engine pressure, due to reduction of the effects of frictional and thermal losses, a larger regenerator can be used. Furthermore, the results show that hydrogen has higher energy efficiency at longer regenerator length due to its low viscosity and high specific heat.