The usage of gas turbines increases rapidly in the electricity production and cogeneration systems in recent years. Decreasing performance of gas turbines causes not only reducing their capacity of electricity production but also increasing production cost. In this study, the thermodynamic analysis of the open cycle gas turbine model is examined. The power output and the thermal efficiency of system are chosen as the performance criteria and the effects of compressor pressure ratio, turbine inlet temperature, isentropic efficiencies and pressure losses on the performance are analyzed. Developed model has been solved by using the computer program written in Visual Basic language and the design parameters giving maximum power and efficiency are determined.