Abstract: A method was proposed to extract acoustic emission signal of gear crack, aiming at detecting fault signal mixed with great noise. Firstly, an adaptive noise compensator was designed to eliminate interference of background noise and therefore improve signal-to-noise ratio. Secondly, a digital bandpass filter was used to further suppress unnecessary signal. Lastly, the signal was decomposed into a finite intrinsic mode functions by empirical mode decomposition. Experiment demonstrated that this method could reconstruct acoustic emission signal of gear crack effectively.