Using 10 mm Q345B steel plate as experimental material, laser-MAG hybrid welding was used to explore the feasibility of high speed backing welding of Y-shaped groove by adjusting welding current, wire feeding speed, welding speed, wire spacing and other hybrid welding parameters. During the experiment, the behavior characteristics of welding arc and droplet transition were analyzed by means of high-speed camera and voltage and current collector. The results show that laser-MAG hybrid welding can realize high speed backing welding with a maximum of 6 mm blunt edge and a minimum angle of 35°groove. The welding speed is 1 m/min, and the adaptability to the gap and the wrong side is better. The matching of laser and arc current has a great influence on the welding stability.