Abstract: Metal magnetic memory(MMM) is a new non-destructive testing method which can make a diagnosis for the ferro-magnetic material in early damaging stage.The wavelet energy spectrum feature of MMM signal for weld cracks.Research shows that,for MMM signals with cracks,the distribution scope of scale-wavelet energy spectrum is wide with a high energy level,and the energy spectrum assumes an exponential attenuation after it reaches a peak,which can be used to estimate whether the sample included crack or not.The space-wavelet energy with crack is higher than that withowt crack,Where the space-wavelet energy spectrum indicates a concentration is the very position of the crack.