Abstract: Pulse YAG laser welding, micro-plasma arc welding and laser+micro-plasma arc hybrid welding were used to weld 304 stainless steel. The structure-borne acoustic emission (AE) signals during welding were detected in real-time to characterize the process of welding. The result showed that the welding effect of laser+micro-plasma arc hybrid welding was better as the defocusing distance was -2 mm. At the same time, the weld appearance showed typical characteristics of hybrid heat source welding. Better weld surface appearance, penetration and width were obtained. As the effect of hybrid heat source welding process was better, the amplitude of AE signals was larger, more uniform and consistent with the cycle of laser-beam heat source, which showed an obvious periodicity of hybrid heat source welding. Consequently, the structure-borne acoustic emission signals detected in welding process was possible to be used to characterize the process of laser+micro-plasma arc hybrid welding.