Today’s modern aircraft is based on air-breathing jet propulsion systems, which use moving fluids as substances to transform energy carried by the fluids into power. Throughout aero-vehicle evolution, improvements have been made to the engine performances and pollutants reduction. These goals were achieved by changing of the bypass ratio (B), fan pressure ratio (Pf), overall pressure ratio (OPR), turbine inlet temperature (TIT) as well as using new materials, production and cooling techniques for both turbines and combustion chamber. Such modifications led to improvements in thermal, propulsive and overall efficiencies, decreases in thrust specific fuel consumption (TSFC) and increase the specific thrust. This paper describes an optimization of a twin spool, separated flow, high bypass turbofan engine and focuses on maximum specific thrust (Fs) with optimum specific fuel consumption (SFC). The two variables, fan pressure ratio (Pf) and bypass ratio (B), were selected as ranges of 1.2-1.9 and 5-8. After that optimum line was investigated that connects the points of maximum Fs and optimum SFC in these ranges that shows optimum engine performance.