Ducted fan noise attenuation method using Herschel–Quincke Tube (HQ Tube) placed on both sides of ducted fan is studied by theoretical and experimental method. The results show that the insertion loss of the system is zero when the effective length of the bypass duct is odd times of half wave length. However, the sound attenuation performance is good when it’s even times. Different from usual HQ Tube, the insertion loss of the system shown in this paper is not zero when the frequency is approaching zero because dipole noise is the main part of the ducted fan noise. The insertion loss of the system when the frequency is approaching zero depends on the length ratio and area ratio between bypass duct and main duct. Comparison to the theoretical method, simulation method and experimental method show that the results are agree with each other at low frequency, but have small differences at middle and high frequency range , the reason is plane wave is not the only wave in the duct .