The AE (acoustic emission) signals of plasma during laser welding were studied using wavelet analysis. Comparing AE signals in welding process with and without joint gap or misalignment problem, the significant differences in AE signals can be observed. The amplitude of low-frequency component of AE signals is fallen down remarkably when the welding defects occur. The same phenomena are also observed in the energy in the frequency band from 1562 Hz to 6250 Hz. Considering that wavelet analysis can decompose the AE signals into several frequency bands, the characteristic information can be extracted, which can be used to implement process-control of laser welding.