This research is based on the thermodynamic performance of a gas turbine power plant. It considered the variation of operating conditions, i.e. the ambient temperature, the compressor outlet temperature, pressure ratio, etc. on the performance of the gas turbine thermal efficiency, turbine work, compressor work, etc. which were derived and analyzed. The Gross (higher) calorific values at constant pressure () heat of combustion in a flow process from state 1 to state 2 was considered and used to analyze our thermal efficiency. The results show that the ambient temperature and air to fuel ratio strongly influence the turbine work, compressor work and thermal efficiency. In addition, the thermal efficiency and power decreases linearly with increase of the ambient temperature. However, the efficiency analyzed when the calorific parameters were considered was higher than the efficiency when the basic thermodynamic theories (first and second law principles) were used. The first ranges between 31% to 33, while the second ranges between 28% to 32% under the same ambient temperature conditions