This paper numerically investigates Coflow Jet (CFJ) active flow control (AFC) for eliminating M2129 serpentine inlet distortion with throat Mach number (Mth) varying from 0.42 to 0.79. The 3D Reynolds Averaged Navier-Stokes (RANS) simulation is conducted with one-equation Spalart-Allmaras (S-A) turbulence model. The CFD simulation is validated with the experiment of AGARD test cases. The predicted total pressure recovery is in good agreement with experiment with the maximum discrepancy less than 1%. The distortion coefficient (DC60) is also in a reasonable agreement with the experiment. The simulation also agrees very well with the experiment for the wall static pressure distribution. For the CFJ S-duct, the horn shaped slot geometry is adopted for the CFJ injection and suction slots to minimize the flow separation caused by CFJ. For all the throat Mach numbers, the engine face distortion coefficient is reduced to less than 1%, virtually eliminated by CFJ. Besides, the total pressure recovery is also significantly enhanced, especially at the high throat Mach number of 0.79. The study also indicates that a higher throat Mach number requires a lower CFJ power coefficient (PC ) to eliminate the flow separation and distortion. This numerical study suggests that it is possible to eliminate S-duct distortion by using CFJ active flow control.