Abstract: In order to understand the mechanism and effect factors of laser-arc hybrid welding,hybrid welding combining CO2 laser and pulsed metal active gas(MAG) arc are taken to weld mild steels,and the effect of various parameters on the welding penetration depth and quality is studied.Laser and arc can be coupled to enhance welding quality if using suitable parameters.Compared with laser welding and MAG welding respectively,hybrid welding penetration can be increased by 1.6 and 2.2 times,while hybrid welding speed can increase 2.7 times that of laser welding.