In this research, we study the effect of the some parameters (gas turbine speed, power turbine speed, mass flow rate of air, mass flow rate of fuel, compression ratio, air to fuel ratio and inlet compressor temperature) on the overall system efficiency, alternator efficiency and the overall heat efficiency of the two shaft gas turbine system, the working fluid was propane. Firstly we checked the experimental results by plotted the (T-S diagram) between the experimental and analytical solution and then we study the effect of the above parameters on the overall system efficiencies. Also we checked the effect of the inlet compressor temperature on the overall gas turbine performance .From these results, we can notes the increasing of the compression ratio and the power turbine speed will increase the overall efficiency, overall heat efficiency and decreasing the alternator efficiency, at the same time is increase the gas turbine efficiency