A novel subsonic airfoil circulation augment technique using co-flow jet(CFJ) to achieve superior aerodynamic performance for subsonic aircraft is proved numerically by CFD simulation. The advantages of co-flow jet airfoil include high lift at high angle of attack, ultra high Cl/Cd at cruise point, and low penalty to the overall cycle efficiency of the airframe-propulsion system. Unlike the conventional circulation control (CC) airfoil which is only suitable for landing and taking off, the CFJ airfoil can be used for the whole flying mission. No blunt leading and trailing edge is required so that the pressure drag is small. No moving parts are needed and make it easy to be implemented and weight less. The jet to enhance the circulation will be recirculated. Compared with the CC airfoil, the recirculating CFJ airfoil will significantly save fuel consumption because: 1) the power required to energize the jet is less; 2) no penalty to the jet engine thrust and efficiency due to the disposed jet mass flow since the jet mass flow is recirculated. For the NACA2415 airfoil studied, at low AOA with moderate momentum jet coefficient, the coflow jet airfoil will not only significantly enhance the lift, but also dramatically reduce the drag, or even generate the negative drag (thrust). The mechanism is that the coflow jet can control the pressure drag by filling the wake, and could generate negative pressure drag greater than the friction drag. This may allow the aircraft to cruise with very high aerodynamic efficiency. At high AOA, both the lift and the drag are significantly higher than the airfoil with no flow control, which may enhance the performance of taking off and landing within short distance.