This study investigates the use of laser-arc hybrid welding to improve the forming quality and mechanical properties of joints in 6 mm thick low carbon steel and medium carbon steel rolled plates. The effects of various process parameters on the welding quality were analyzed, and hardness and tensile tests were conducted on samples with optimized parameters to elucidate the reasons for enhanced mechanical properties. The experimental results show that the arc heat input mainly affects the droplet transition form during welding. With the gradual increase of arc heat input, the droplet transfer changes from unstable short circuit transfer to stable droplet transfer, and the quality of weld formation is significantly improved. The depth of the weld is mainly affected by the laser heat input. The weld is considered to have the best quality when the laser heat input reaches 247.5 kJ/m, and completely penetrate. During the welding process, recrystallization occurs in the welded joint area due to the high temperature thermal cycle, resulting in a large number of fine subcrystals and dislocations, which is the fundamental reason for the improvement of mechanical properties of the welded joint.