The flow field and aerodynamic design characteristics of core driven fan stage(CDFS) were simulated and analyzed with modified Denton code.The results show that: 1)adjustable inlet guide vane(IGV) is needed to achieve the switch of different working modes;2) the conflict between high tip speed and low aerodynamic loading restrains the efficiency of CDFS;3) IGV outlet swirl distribution and switch mode have remarkable effects on CDFS performance;4) the challenge in the aerodynamic design of CDFS rotor is the shock loss in single bypass mode;5) the change in distribution and magnitude of CDFS stator inlet flow angle is the main challenge in CDFS stator design.