For the low noise target feature of dieselelectric hybrid power unit which was used as the power of high mobility ground unmanned platform, the research on noise source recognition and noise reduction was carried out. The noise level of original state and the basic contrast of each radiation plane were acquired by direct sampling test of microphones, and the noise source recognition and high-contribution location of main radiation plane was obtained by irregular acoustic array test based on the principle of beamforming. The actual effect of surface sound pressure level reduced by 2.8-3.0 dB, the corresponding sound pressure reduced by 27%-29% and sound power reduced by 48%-50% based on the measures such as covering the noise source, spraying the noise source reduction coating and so on. Finally, the effectiveness of noise recognition method and noise reduction measure was verified.