Abstract: The Red Lake high speed photography system was adopted to observe the wire transition behavior in scanning laser hot wire welding. The influences of laser-arc distance, scanning laser and hot wire on welding wire transition behavior were explored.The results revealed that liquid bridge transition could be achieved when the laser-arc distance varied from-1 mm to 1 mm; when scanning laser was added, the welding wire turned to swing when transited into the welding pool, and with the increasing of the oscillating amplitude of the scanning laser, the wire swing amplitude increased at first and then decreased; when hot wire was heated, the wire transition behavior included liquid bridge transition, droplet metal transition and arc transition; compared to cold wire, the wire swing amplitude decreased.