Abstract: A frequency compensation beamforming method is proposed which aims to locate aeroacoustic sources of helicopter rotor in forward flight.The sources with frequency fluctuation cannot be located by state-of-art frequency domain beamforming methods,which leads to incorrect source mapping results.The frequency fluctuation of source signal is compensated in the time domain according to the non-constant relative speed between the solid surface of rotating blades and the flow,and an equivalent signal frequency is used in the accurate location locating of the rotary motion sources.The simulation results indicate that sources with frequency fluctuation amplitude of 127 Hz could be located by the proposed method.In the wind tunnel test of the rotor model,the maximum energy position of the sound source in the acoustic imaging results using the proposed frequency-domain beamforming method is near the rotating track,while the results using the beamforming method without frequency correction cannot accurately show the position of the sound source.This method extends the assumption of single frequency sound source in the frequency domain beamforming method,and realizes the beamforming of rotary motion sound source in the state of frequency fluctuation,which is suitable for the localization of rotor aerodynamic noise source in the state of forward flight.