This study investigates the weld formation of 20 mm thick EH36 high-strength steel using laser-arc hybrid welding. The weld forming characteristics under various laser powers, welding speeds, and wire feeding speeds were examined under a non-groove butt joint configuration. The arc and plasma characteristics during welding were analyzed and observed through high-speed photography. The results show that the fluctuation of weld penetration increases with the increase of laser power. The increase of laser power enhances the heating and radiation of welding wire, resulting in the acceleration of welding wire melting rate; Increasing the welding speed in a small range has a certain inhibiting effect on the back hump defect, and is conducive to reducing the degree of underfill; In high current welding, the concavity of the underfill decreases first and then increases with the increase of wire feeding speed. The arc force generated at higher wire feeding speed and the disturbance of the welding wire end to the weld pool are the main reasons for the underfill and poor formation of the weld.