Abstract: Characteristic analysis of the acoustic emission (AE) signal accompanying welding process by way of experiment is a prerequisite for realizing online detection of the welding crack. An AE signal characteristic analysis method based on harmonic extraction is proposed. Combining with an experiment on AE signals during the welding process, the valid extraction and frequency spectrum analysis are performed for AE signals collected in welding process. The AE signals frequency domain characteristics of the corresponding excitation source of friction, the welding arc shock and the welding structure crack are obtained respectively, which provide basic data and reference for realizing AE online detection of the welding crack.