Pressure pulsation of axial flow fan’〖KG-*2〗s inside flow was measured by dynamic pressure sensor，the gasstructure coupled noise of counterrotating axial flow fan was studied through a new perspective. The pressure pulsation and noise in the internal flow field of counterrotating axial flow fan were measured by experimental method. Meanwhile, the gasstructure coupled noise characteristics were investigated by numerical simulation. It is revealed that the gas pressure pulsation, separated flows and vortex motion in the internal flow field caused by the gasstructure coupled function are the main reasons. Furthermore, the noise reduction on fan blade with bionic structure was carried out. The noise was reduced 2.5 dB (A) by using serrated blade.